WEBDAV Working Group Y.Y. Goland, Microsoft
INTERNET DRAFT E.J. Whitehead, Jr., UC Irvine
A. Faizi, Netscape
S.R. Carter, Novell
D. Jensen, Novell
Expires September, 1998 April 7, 1998
Extensions for Distributed Authoring on the World Wide Web -- WEBDAV
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or made obsolete by other
documents at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress".
To view the entire list of current Internet-Drafts, please check
the "1id-abstracts.txt" listing contained in the Internet-Drafts
Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net
(Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au
(Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu
(US West Coast).
Distribution of this document is unlimited. Please send comments to
the Distributed Authoring and Versioning (WEBDAV) working group at
, which may be joined by sending a message
with subject "subscribe" to .
Discussions of the WEBDAV working group are archived at
.
Abstract
This document specifies a set of methods, headers, and content-types
ancillary to HTTP/1.1 for the management of resource properties,
creation and management of resource collections, namespace
manipulation, and resource locking (collision avoidance).
Goland et al. [Page 1]
INTERNET-DRAFT WebDAV April 7, 1998
Contents
STATUS OF THIS MEMO ..................................................1
ABSTRACT .............................................................1
CONTENTS .............................................................2
1 INTRODUCTION .......................................................7
2 NOTATIONAL CONVENTIONS .............................................8
3 DATA MODEL FOR RESOURCE PROPERTIES .................................8
3.1 The Resource Property Model .....................................8
3.2 Existing Metadata Proposals .....................................9
3.3 Properties and HTTP Headers ....................................10
3.4 Property Values ................................................10
3.5 Property Names .................................................10
3.6 Media Independent Links ........................................11
4 COLLECTIONS OF WEB RESOURCES ......................................11
4.1 Collection Resources ...........................................11
4.2 Creation and Retrieval of Collection Resources .................12
4.3 HTTP URL Namespace Model .......................................12
4.4 Source Resources and Output Resources ..........................12
5 LOCKING ...........................................................13
5.1 Exclusive Vs. Shared Locks .....................................14
5.2 Required Support ...............................................15
5.3 Lock Tokens ....................................................15
5.4 opaquelocktoken Lock Token URI Scheme ..........................15
5.5 Lock Capability Discovery ......................................16
5.6 Active Lock Discovery ..........................................16
5.7 Usage Considerations ...........................................16
6 WRITE LOCK ........................................................17
6.1 Methods Restricted by Write Locks ..............................17
6.2 Write Locks and Properties .....................................18
6.3 Write Locks and Null Resources .................................18
6.4 Write Locks and Collections ....................................18
6.5 Write Locks and the If Request Header ..........................19
6.5.1 Example - Write Lock .........................................19
6.6 Write Locks and COPY/MOVE ......................................20
6.7 Refreshing Write Locks .........................................20
7 HTTP METHODS FOR DISTRIBUTED AUTHORING ............................20
7.1 PROPFIND .......................................................21
7.1.1 Example - Retrieving Named Properties ........................22
7.1.2 Example - Using allprop to Retrieve All Properties ...........23
7.1.3 Example - Using propname to Retrieve all Property Names ......25
7.2 PROPPATCH ......................................................27
7.2.1 Status Codes for use with Multi-Status .......................27
7.2.2 Example - PROPPATCH ..........................................28
7.3 MKCOL Method ...................................................29
7.3.1 Request ......................................................29
Goland et al. [Page 2]
INTERNET-DRAFT WebDAV April 7, 1998
7.3.2 Response Codes ...............................................30
7.3.3 Example - MKCOL ..............................................30
7.4 GET, HEAD for Collections ......................................31
7.5 POST for Collections ...........................................31
7.6 DELETE .........................................................31
7.6.1 DELETE for Non-Collection Resources ..........................31
7.6.2 DELETE for Collections .......................................31
7.7 PUT ............................................................32
7.7.1 PUT for Non-Collection Resources .............................32
7.7.2 PUT for Collections ..........................................33
7.8 COPY Method ....................................................33
7.8.1 COPY for HTTP/1.1 resources ..................................33
7.8.2 COPY for Properties ..........................................34
7.8.3 COPY for Collections .........................................34
7.8.4 COPY and the Overwrite Header ................................35
7.8.5 Status Codes .................................................35
7.8.6 Example - COPY with Overwrite ................................36
7.8.7 Example - COPY with No Overwrite .............................36
7.8.8 Example - COPY of a Collection ...............................36
7.9 MOVE Method ....................................................37
7.9.1 MOVE for Properties ..........................................37
7.9.2 MOVE for Collections .........................................38
7.9.3 MOVE and the Overwrite Header ................................38
7.9.4 Status Codes .................................................39
7.9.5 Example - MOVE of a Non-Collection ...........................39
7.9.6 Example - MOVE of a Collection ...............................39
7.10 LOCK Method ...................................................40
7.10.1 Operation ...................................................40
7.10.2 The Effect of Locks on Properties and Collections ...........41
7.10.3 Locking Replicated Resources ................................41
7.10.4 Depth and Locking ...........................................41
7.10.5 Interaction with other Methods ..............................42
7.10.6 Lock Compatibility Table ....................................42
7.10.7 Status Codes ................................................42
7.10.8 Example - Simple Lock Request ...............................43
7.10.9 Example - Refreshing a Write Lock ...........................44
7.10.10 Example - Multi-Resource Lock Request ......................45
7.11 UNLOCK Method .................................................46
7.11.1 Example - UNLOCK ............................................46
8 HTTP HEADERS FOR DISTRIBUTED AUTHORING ............................47
8.1 DAV Header .....................................................47
8.2 Depth Header ...................................................47
8.3 Destination Header .............................................48
8.4 If Header ......................................................48
8.4.1 No-tag-list Production .......................................49
Goland et al. [Page 3]
INTERNET-DRAFT WebDAV April 7, 1998
8.4.2 Tagged-list Production .......................................49
8.4.3 not Production ...............................................50
8.4.4 Matching Function ............................................50
8.4.5 If Header and Non-DAV Compliant Proxies ......................51
8.5 Lock-Token Request Header ......................................51
8.6 Overwrite Header ...............................................51
8.7 Status-URI Response Header .....................................51
8.8 Timeout Request Header .........................................52
9 STATUS CODE EXTENSIONS TO HTTP/1.1 ................................53
9.1 102 Processing .................................................53
9.2 207 Multi-Status ...............................................53
9.3 422 Unprocessable Entity .......................................53
9.4 423 Locked .....................................................53
9.5 424 Method Failure .............................................53
9.6 425 Insufficient Space on Resource .............................53
10 MULTI-STATUS RESPONSE ............................................54
11 XML ELEMENT DEFINITIONS ..........................................54
11.1 activelock XML Element ........................................54
11.1.1 depth XML Element ...........................................54
11.1.2 locktoken XML Element .......................................54
11.1.3 timeout XML Element .........................................54
11.2 collection XML Element ........................................55
11.3 href XML Element ..............................................55
11.4 link XML Element ..............................................55
11.4.1 dst XML Element .............................................55
11.4.2 src XML Element .............................................55
11.5 lockentry XML Element .........................................56
11.6 lockinfo XML Element ..........................................56
11.7 lockscope XML Element .........................................56
11.7.1 exclusive XML Element .......................................56
11.7.2 shared XML Element ..........................................56
11.8 locktype XML Element ..........................................56
11.8.1 write XML Element ...........................................57
11.9 multistatus XML Element .......................................57
11.9.1 response XML Element ........................................57
11.9.2 responsedescription XML Element .............................58
11.10 owner XML Element ............................................58
11.11 prop XML element .............................................58
11.12 propertybehavior XML element .................................59
11.12.1 keepalive XML element ......................................59
11.12.2 omit XML element ...........................................59
11.13 propertyupdate XML element ...................................60
11.13.1 remove XML element .........................................60
11.13.2 set XML element ............................................60
11.14 propfind XML Element .........................................60
Goland et al. [Page 4]
INTERNET-DRAFT WebDAV April 7, 1998
11.14.1 allprop XML Element ........................................61
11.14.2 propname XML Element .......................................61
12 DAV PROPERTIES ...................................................61
12.1 creationdate Property .........................................61
12.2 displayname Property ..........................................61
12.3 getcontentlanguage Property ...................................62
12.4 getcontentlength Property .....................................62
12.5 getcontenttype Property .......................................62
12.6 getetag Property ..............................................62
12.7 getlastmodified Property ......................................63
12.8 lockdiscovery Property ........................................63
12.8.1 Example - Retrieving the lockdiscovery Property .............63
12.9 resourcetype Property .........................................64
12.10 source Property ..............................................65
12.10.1 Example - A source Property ................................65
12.11 supportedlock Property .......................................66
12.11.1 Example - Retrieving the supportedlock Property ............66
13 DAV XML PROCESSING INSTRUCTIONS ..................................67
14 DAV COMPLIANCE CLASSES ...........................................67
14.1 Class 1 .......................................................68
14.2 Class 2 .......................................................68
15 INTERNATIONALIZATION CONSIDERATIONS ..............................68
16 SECURITY CONSIDERATIONS ..........................................69
16.1 Authentication of Clients .....................................69
16.2 Denial of Service .............................................70
16.3 Security through Obscurity ....................................70
16.4 Privacy Issues Connected to Locks .............................71
16.5 Privacy Issues Connected to Properties ........................71
16.6 Reduction of Security due to Source Link ......................71
17 IANA CONSIDERATIONS ..............................................71
18 TERMINOLOGY ......................................................72
19 COPYRIGHT ........................................................73
20 INTELLECTUAL PROPERTY ............................................73
21 ACKNOWLEDGEMENTS .................................................74
22 REFERENCES .......................................................75
22.1 Normative References ..........................................75
22.2 Informational References ......................................75
23 AUTHORS' ADDRESSES ...............................................77
24 APPENDICES .......................................................78
24.1 Appendix 1 - WebDAV Document Type Definition ..................78
24.2 Appendix 2 - ISO 8601 Date and Time Profile ...................79
24.3 Appendix 3 - Notes on Processing XML Elements .................80
24.3.1 Notes on Empty XML Elements .................................80
24.3.2 Notes on Illegal XML Processing .............................80
24.4 Appendix 4 -- XML Namespaces for WebDAV .......................82
Goland et al. [Page 5]
INTERNET-DRAFT WebDAV April 7, 1998
24.4.1 Introduction ................................................82
24.4.2 Namespace Declaration PI ....................................83
24.4.3 Placing Declarations in Documents ...........................84
24.4.4 Prolog with Namespace Declarations ..........................84
24.4.5 Qualified Names .............................................84
24.4.6 Universal Names .............................................85
24.4.7 Using Qualified Names .......................................85
24.4.8 Processing instruction ......................................85
24.4.9 Scope and Meaning of Qualified Names ........................85
Goland et al. [Page 6]
INTERNET-DRAFT WebDAV April 7, 1998
1 Introduction
This document describes an extension to the HTTP/1.1 protocol that
allows clients to perform remote web content authoring operations.
This extension provides a coherent set of methods, headers, request
entity body formats, and response entity body formats that provide
operations for:
Properties: The ability to create, remove, and query information
about Web pages, such as their authors, creation dates, etc. Also,
the ability to link pages of any media type to related pages.
Collections: The ability to create sets of related documents and to
retrieve a hierarchical membership listing (like a directory listing
in a file system).
Locking: The ability to keep more than one person from working on a
document at the same time. This prevents the "lost update problem,"
in which modifications are lost as first one author then another
writes changes without merging the other author's changes.
Namespace Operations: The ability to instruct the server to copy and
move Web resources.
Requirements and rationale for these operations are described in a
companion document, "Requirements for a Distributed Authoring and
Versioning Protocol for the World Wide Web" [Slein et al., 1998].
The sections below provide a detailed introduction to resource
properties (section 3), collections of resources (section 4), and
locking operations (section 5). These sections introduce the
abstractions manipulated by the WebDAV-specific HTTP methods
described in section 7, "HTTP Methods for Distributed Authoring".
In HTTP/1.1, method parameter information was exclusively encoded in
HTTP headers. Unlike HTTP/1.1, WebDAV, encodes method parameter
information either in an Extensible Markup Language (XML) [Bray,
Paoli, Sperberg-McQueen, 1998] request entity body, or in an HTTP
header. The use of XML to encode method parameters was motivated by
the ability to add extra XML elements to existing structures,
providing extensibility, and by XML's ability to encode information
in ISO 10646 character sets, providing internationalization support.
As a rule of thumb, parameters are encoded in XML entity bodies when
they have unbounded length, or when they may be shown to a human
user and hence require encoding in an ISO 10646 character set.
Otherwise, parameters are encoded within HTTP headers. Section 8
describes the new HTTP headers used with WebDAV methods.
In addition to encoding method parameters, XML is used in WebDAV to
encode the responses from methods, providing the extensibility and
Goland et al. [Page 7]
INTERNET-DRAFT WebDAV April 7, 1998
internationalization advantages of XML for method output, as well as
input.
XML elements used in this specification are defined in section 11.
The XML namespace extension (Appendix 4) is also used in this
specification in order to allow for new XML elements to be added
without fear of colliding with other element names.
While the status codes provided by HTTP/1.1 are sufficient to
describe most error conditions encountered by WebDAV methods, there
are some errors that do not fall neatly into the existing
categories. New status codes developed for the WebDAV methods are
defined in section 9. Since some WebDAV methods may operate over
many resources, the Multi-Status response has been introduced to
return status information for multiple resources. The Multi-Status
response is described in section 10.
WebDAV employs the property mechanism to store information about the
current state of the resource. For example, when a lock is taken
out on a resource, a lock information property describes the current
state of the lock. Section 12 defines the properties used within the
WebDAV specification.
Finishing off the specification are sections on what it means to be
compliant with this specification (section 14), on
internationalization support (section 15), and on security (section
16).
2 Notational Conventions
Since this document describes a set of extensions to the HTTP/1.1
protocol, the augmented BNF used herein to describe protocol
elements is exactly the same as described in section 2.1 of
[Fielding et al., 1997]. Since this augmented BNF uses the basic
production rules provided in section 2.2 of [Fielding et al., 1997],
these rules apply to this document as well.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [Bradner,
1997].
3 Data Model for Resource Properties
3.1 The Resource Property Model
Properties are pieces of data that describe the state of a resource.
Properties are data about data.
Properties are used in distributed authoring environments to provide
for efficient discovery and management of resources. For example, a
Goland et al. [Page 8]
INTERNET-DRAFT WebDAV April 7, 1998
'subject' property might allow for the indexing of all resources by
their subject, and an 'author' property might allow for the
discovery of what authors have written which documents.
The DAV property model consists of name/value pairs. The name of a
property identifies the property's syntax and semantics, and
provides an address by which to refer to its syntax and semantics.
There are two categories of properties: "live" and "dead". A live
property has its syntax and semantics enforced by the server. Live
properties include cases where a) the value of a property is read-
only, maintained by the server, and b) the value of the property is
maintained by the client, but the server performs syntax checking on
submitted values. A dead property has its syntax and semantics
enforced by the client; the server merely records the value of the
property verbatim.
3.2 Existing Metadata Proposals
Properties have long played an essential role in the maintenance of
large document repositories, and many current proposals contain some
notion of a property, or discuss web metadata more generally. These
include PICS [Miller et al., 1996], PICS-NG, XML, Web Collections,
and several proposals on representing relationships within HTML.
Work on PICS-NG and Web Collections has been subsumed by the
Resource Definition Framework (RDF) metadata activity of the World
Wide Web Consortium. RDF consists of a network-based data model and
an XML representation of that model.
Some proposals come from a digital library perspective. These
include the Dublin Core [Weibel et al., 1995] metadata set and the
Warwick Framework [Lagoze, 1996], a container architecture for
different metadata schemas. The literature includes many examples
of metadata, including MARC [MARC, 1994], a bibliographic metadata
format, and RFC 1807 [Lasher, Cohen, 1995], a technical report
bibliographic format employed by the Dienst system. Additionally,
the proceedings from the first IEEE Metadata conference describe
many community-specific metadata sets.
Participants of the 1996 Metadata II Workshop in Warwick, UK
[Lagoze, 1996], noted that "new metadata sets will develop as the
networked infrastructure matures" and "different communities will
propose, design, and be responsible for different types of
metadata." These observations can be corroborated by noting that
many community-specific sets of metadata already exist, and there is
significant motivation for the development of new forms of metadata
as many communities increasingly make their data available in
digital form, requiring a metadata format to assist data location
and cataloging.
Goland et al. [Page 9]
INTERNET-DRAFT WebDAV April 7, 1998
3.3 Properties and HTTP Headers
Properties already exist, in a limited sense, in HTTP message
headers. However, in distributed authoring environments a
relatively large number of properties are needed to describe the
state of a resource, and setting/returning them all through HTTP
headers is inefficient. Thus a mechanism is needed which allows a
principal to identify a set of properties in which the principal is
interested and to set or retrieve just those properties.
3.4 Property Values
The value of a property is, at minimum, well formed XML.
XML has been chosen because it is a flexible, self-describing,
structured data format that supports rich schema definitions, and
because of its support for multiple character sets. XML's self-
describing nature allows any property's value to be extended by
adding new elements. Older clients will not break when they
encounter extensions because they will still have the data specified
in the original schema and will ignore elements they do not
understand. XML's support for multiple character sets allows any
human-readable property to be encoded and read in a character set
familiar to the user.
3.5 Property Names
A property name is a universally unique identifier that is
associated with a schema that provides information about the syntax
and semantics of the property.
Because a property's name is universally unique, clients can depend
upon consistent behavior for a particular property across multiple
resources, so long as that property is "live" on the resources in
question.
The XML namespace mechanism, which is based on URIs, is used to name
properties because it prevents namespace collisions and provides for
varying degrees of administrative control.
The property namespace is flat; that is, no hierarchy of properties
is explicitly recognized. Thus, if a property A and a property A/B
exist on a resource, there is no recognition of any relationship
between the two properties. It is expected that a separate
specification will eventually be produced which will address issues
relating to hierarchical properties.
Finally, it is not possible to define the same property twice on a
single resource, as this would cause a collision in the resource's
property namespace.
Goland et al. [Page 10]
INTERNET-DRAFT WebDAV April 7, 1998
3.6 Media Independent Links
Although HTML resources support links to other resources, the Web
needs more general support for links between resources of any media
type. WebDAV provides such links. A WebDAV link is a special type
of property value, formally defined in section 11.4, that allows
typed connections to be established between resources of any media
type. The property value consists of source and destination Uniform
Resource Locators (URLs); the property name identifies the link
type.
4 Collections of Web Resources
This section provides a description of a new type of Web resource,
the collection, and discusses its interactions with the HTTP URL
namespace. The purpose of a collection resource is to model
collection-like objects (e.g., file system directories) within a
server's namespace.
All DAV compliant resources MUST support the HTTP URL namespace
model specified herein.
4.1 Collection Resources
A collection is a resource whose state consists of at least a list
of internal members and a set of properties, but which may have
additional state such as entity bodies returned by GET. An internal
member resource MUST have a URI that is immediately relative to the
base URI of the collection. That is, the internal member's URI is
equal to the parent collection's URI plus an additional segment
where segment is defined in section 3.2.1 of RFC 2068 [Fielding et
al., 1996].
Any given internal member MUST only belong to the collection once,
i.e., it is illegal to have multiple instances of the same URI in a
collection. Properties defined on collections behave exactly as do
properties on non-collection resources.
WebDAV servers MUST treat HTTP URL namespaces as collections,
regardless of whether they were created with the MKCOL method
described in section 7.3.
There is a standing convention that when a collection is referred to
by its name without a trailing slash, the trailing slash is
automatically appended. Due to this, a resource may accept a URI
without a trailing "/" to point to a collection. In this case it
SHOULD return a content-location header in the response pointing to
the URL ending with the "/". For example, if a client invokes a
method on http://foo.bar/blah (no trailing slash), the resource
http://foo.bar/blah/ (trailing slash) may respond as if the
operation were invoked on it, and should return a content-location
Goland et al. [Page 11]
INTERNET-DRAFT WebDAV April 7, 1998
header with http://foo.bar/blah/ in it. In general clients SHOULD
use the "/" form of collection names.
4.2 Creation and Retrieval of Collection Resources
This document specifies the MKCOL method to create new collection
resources, rather than using the existing HTTP/1.1 PUT or POST
method, for the following reasons:
In HTTP/1.1, the PUT method is defined to store the request body at
the location specified by the Request-URI. While a description
format for a collection can readily be constructed for use with PUT,
the implications of sending such a description to the server are
undesirable. For example, if a description of a collection that
omitted some existing resources were PUT to a server, this might be
interpreted as a command to remove those members. This would extend
PUT to perform DELETE functionality, which is undesirable since it
changes the semantics of PUT, and makes it difficult to control
DELETE functionality with an access control scheme based on methods.
While the POST method is sufficiently open-ended that a "create a
collection" POST command could be constructed, this is undesirable
because it would be difficult to separate access control for
collection creation from other uses of POST.
The exact definition of the behavior of GET and PUT on collections
is defined later in this document.
4.3 HTTP URL Namespace Model
The HTTP URL Namespace is a hierarchical namespace where the
hierarchy is delimited with the "/" character. DAV compliant
resources MUST maintain the consistency of the HTTP URL namespace.
For example, if the collection http://www.foo.bar.org/a/ exists, but
http://www.foo.bar.org/a/b/ does not exist, an attempt to create
http://www.foo.bar.org/a/b/c must fail.
4.4 Source Resources and Output Resources
For many resources, the entity returned by a GET method exactly
matches the persistent state of the resource, for example, a GIF
file stored on a disk. For this simple case, the URL at which a
resource is accessed is identical to the URL at which the source
(the persistent state) of the resource is accessed. This is also
the case for HTML source files that are not processed by the server
prior to transmission.
However, the server can sometimes process HTML resources before they
are transmitted as a return entity body. For example, a server-
side-include directive within an HTML file might instruct a server
to replace the directive with another value, such as the current
date. In this case, what is returned by GET (HTML plus date)
Goland et al. [Page 12]
INTERNET-DRAFT WebDAV April 7, 1998
differs from the persistent state of the resource (HTML plus
directive). Typically there is no way to access the HTML resource
containing the unprocessed directive.
Sometimes the entity returned by GET is the output of a data-
producing process that is described by one or more source resources
(that may not even have a location in the URL namespace). A single
data-producing process may dynamically generate the state of a
potentially large number of output resources. An example of this is
a CGI script that describes a "finger" gateway process that maps
part of the namespace of a server into finger requests, such as
http://www.foo.bar.org/finger_gateway/user@host.
In the absence of distributed authoring capabilities, it is
acceptable to have no mapping of source resource(s) to the URI
namespace. In fact, preventing access to the source resource(s) has
desirable security benefits. However, if remote editing of the
source resource(s) is desired, the source resource(s) should be
given a location in the URI namespace. This source location should
not be one of the locations at which the generated output is
retrievable, since in general it is impossible for the server to
differentiate requests for source resources from requests for
process output resources. There is often a many-to-many
relationship between source resources and output resources.
On WebDAV compliant servers the URI of the source resource(s) may be
stored in a link on the output resource with type DAV:source (see
section 12.10 for a description of the source link property).
Storing the source URIs in links on the output resources places the
burden of discovering the source on the authoring client. Note that
the value of a source link is not guaranteed to point to the correct
source. Source links may break or incorrect values may be entered.
Also note that not all servers will allow the client to set the
source link value. For example a server which generates source
links on the fly for its CGI files will most likely not allow a
client to set the source link value.
5 Locking
The ability to lock a resource provides a mechanism for serializing
access to that resource. Using a lock, an authoring client can
provide a reasonable guarantee that another principal will not
modify a resource while it is being edited. In this way, a client
can prevent the "lost update" problem.
This specification allows locks to vary over two client-specified
parameters, the number of principals involved (exclusive vs. shared)
and the type of access to be granted. This document defines locking
for only one access type, write. However, the syntax is extensible,
and permits the eventual specification of locking for other access
types.
Goland et al. [Page 13]
INTERNET-DRAFT WebDAV April 7, 1998
5.1 Exclusive Vs. Shared Locks
The most basic form of lock is an exclusive lock. This is a lock
where the access right in question is only granted to a single
principal. The need for this arbitration results from a desire to
avoid having to merge results.
However, there are times when the goal of a lock is not to exclude
others from exercising an access right but rather to provide a
mechanism for principals to indicate that they intend to exercise
their access rights. Shared locks are provided for this case. A
shared lock allows multiple principals to receive a lock. Hence any
principal with appropriate access can get the lock.
With shared locks there are two trust sets that affect a resource.
The first trust set is created by access permissions. Principals
who are trusted, for example, may have permission to write to the
resource. Among those who have access permission to write to the
resource, the set of principals who have taken out a shared lock
also must trust each other, creating a (typically) smaller trust set
within the access permission write set.
Starting with every possible principal on the Internet, in most
situations the vast majority of these principals will not have write
access to a given resource. Of the small number who do have write
access, some principals may decide to guarantee their edits are free
from overwrite conflicts by using exclusive write locks. Others may
decide they trust their collaborators will not overwrite their work
(the potential set of collaborators being the set of principals who
have write permission) and use a shared lock, which informs their
collaborators that a principal may be working on the resource.
The WebDAV extensions to HTTP do not need to provide all of the
communications paths necessary for principals to coordinate their
activities. When using shared locks, principals may use any out of
band communication channel to coordinate their work (e.g., face-to-
face interaction, written notes, post-it notes on the screen,
telephone conversation, Email, etc.) The intent of a shared lock is
to let collaborators know who else may be working on a resource.
Shared locks are included because experience from web distributed
authoring systems has indicated that exclusive locks are often too
rigid. An exclusive lock is used to enforce a particular editing
process: take out an exclusive lock, read the resource, perform
edits, write the resource, release the lock. This editing process
has the problem that locks are not always properly released, for
example when a program crashes, or when a lock owner leaves without
unlocking a resource. While both timeouts and administrative action
can be used to remove an offending lock, neither mechanism may be
available when needed; the timeout may be long or the administrator
may not be available.
Goland et al. [Page 14]
INTERNET-DRAFT WebDAV April 7, 1998
5.2 Required Support
A WebDAV compliant server is not required to support locking in any
form. If the server does support locking it may choose to support
any combination of exclusive and shared locks for any access types.
The reason for this flexibility is that locking policy strikes to
the very heart of the resource management and versioning systems
employed by various storage repositories. These repositories
require control over what sort of locking will be made available.
For example, some repositories only support shared write locks while
others only provide support for exclusive write locks while yet
others use no locking at all. As each system is sufficiently
different to merit exclusion of certain locking features, this
specification leaves locking as the sole axis of negotiation within
WebDAV.
5.3 Lock Tokens
A lock token is a type of state token, represented as a URI, which
identifies a particular lock. A lock token is returned by every
successful LOCK operation in the lockdiscovery property in the
response body, and can also be found through lock discovery on a
resource.
Lock token URIs MUST be unique across all resources for all time.
This uniqueness constraint allows lock tokens to be submitted across
resources and servers without fear of confusion.
This specification provides a lock token URI scheme called
opaquelocktoken that meets the uniqueness requirements. However
resources are free to return any URI scheme so long as it meets the
uniqueness requirements.
Having a lock token provides no special access rights. Anyone can
find out anyone else's lock token by performing lock discovery.
Locks MUST be enforced based upon whatever authentication mechanism
is used by the server, not based on the secrecy of the token values.
5.4 opaquelocktoken Lock Token URI Scheme
The opaquelocktoken URI scheme is designed to be unique across all
resources for all time. Due to this uniqueness quality, a client
may submit an opaque lock token in an If header on a resource other
than the one that returned it.
All resources MUST recognize the opaquelocktoken scheme and, at
minimum, recognize that the lock token does not refer to an
outstanding lock on the resource.
In order to guarantee uniqueness across all resources for all time
the opaquelocktoken requires the use of the Universally Unique
Goland et al. [Page 15]
INTERNET-DRAFT WebDAV April 7, 1998
Identifier (UUID, also known as a Globally Unique Identifier, or
GUID) mechanism, as described in [Leach, Salz, 1998].
Opaquelocktoken generators, however, have a choice of how they
create these tokens. They can either generate a new UUID for every
lock token they create or they can create a single UUID and then add
extension characters. If the second method is selected then the
program generating the extensions MUST guarantee that the same
extension will never be used twice with the associated UUID.
OpaqueLockToken-URI = "opaquelocktoken:" UUID [Extension] ; The
UUID production is the string form of a UUID, as defined in [Leach,
Salz, 1998]. Note that white space (LWS) is not allowed between
elements of this production.
Extension = path ; path is defined in section 3.2.1 of RFC 2068
[Fielding et al., 1996]
5.5 Lock Capability Discovery
Since server lock support is optional, a client trying to lock a
resource on a server can either try the lock and hope for the best,
or perform some form of discovery to determine what lock
capabilities the server supports. This is known as lock capability
discovery. Lock capability discovery differs from discovery of
supported access control types, since there may be access control
types without corresponding lock types. A client can determine what
lock types the server supports by retrieving the supportedlock
property.
Any DAV compliant resource that supports the LOCK method MUST
support the supportedlock property.
5.6 Active Lock Discovery
If another principal locks a resource that a principal wishes to
access, it is useful for the second principal to be able to find out
who the first principal is. For this purpose the lockdiscovery
property is provided. This property lists all outstanding locks,
describes their type, and where available, provides their lock
token.
Any DAV compliant resource that supports the LOCK method MUST
support the lockdiscovery property.
5.7 Usage Considerations
Although the locking mechanisms specified here provide some help in
preventing lost updates, they cannot guarantee that updates will
never be lost. Consider the following scenario:
Goland et al. [Page 16]
INTERNET-DRAFT WebDAV April 7, 1998
Two clients A and B are interested in editing the resource
'index.html'. Client A is an HTTP client rather than a WebDAV
client, and so does not know how to perform locking.
Client A doesn't lock the document, but does a GET and begins
editing.
Client B does LOCK, performs a GET and begins editing.
Client B finishes editing, performs a PUT, then an UNLOCK.
Client A performs a PUT, overwriting and losing all of B's changes.
There are several reasons why the WebDAV protocol itself cannot
prevent this situation. First, it cannot force all clients to use
locking because it must be compatible with HTTP clients that do not
comprehend locking. Second, it cannot require servers to support
locking because of the variety of repository implementations, some
of which rely on reservations and merging rather than on locking.
Finally, being stateless, it cannot enforce a sequence of operations
like LOCK / GET / PUT / UNLOCK.
WebDAV servers that support locking can reduce the likelihood that
clients will accidentally overwrite each other's changes by
requiring clients to lock resources before modifying them. Such
servers would effectively prevent HTTP 1.0 and HTTP 1.1 clients from
modifying resources.
WebDAV clients can be good citizens by using a lock / retrieve /
write /unlock sequence of operations (at least by default) whenever
they interact with a WebDAV server that supports locking.
HTTP 1.1 clients can be good citizens, avoiding overwriting other
clients' changes, by using entity tags in If-Match headers with any
requests that would modify resources.
Information managers may attempt to prevent overwrites by
implementing client-side procedures requiring locking before
modifying WebDAV resources.
6 Write Lock
This section describes the semantics specific to the write lock
type. The write lock is a specific instance of a lock type, and is
the only lock type described in this specification.
6.1 Methods Restricted by Write Locks
A write lock MUST prevent a principal without the lock from
successfully executing a PUT, POST, PROPPATCH, LOCK, UNLOCK, MOVE,
DELETE, or MKCOL on the locked resource. All other current methods,
GET in particular, function independent of the lock.
Note, however, that as new methods are created it will be necessary
to specify how they interact with a write lock.
Goland et al. [Page 17]
INTERNET-DRAFT WebDAV April 7, 1998
6.2 Write Locks and Properties
While those without a write lock may not alter a property on a
resource it is still possible for the values of live properties to
change, even while locked, due to the requirements of their schemas.
Only dead properties and live properties defined to respect locks
are guaranteed not to change while write locked.
6.3 Write Locks and Null Resources
It is possible to assert a write lock on a null resource in order to
lock the name.
A write locked null resource, referred to as a lock-null resource,
MUST respond with a 404 Not Found or 405 Method Not Allowed to any
HTTP/1.1 or DAV methods except for PUT, MKCOL, OPTIONS, PROPFIND,
LOCK, and UNLOCK. A lock-null resource MUST appear as a member of
its parent collection. Additionally the lock-null resource MUST
have defined on it all mandatory DAV properties. Most of these
properties, such as all the get* properties, will have no value as a
lock-null resource does not support the GET method. Lock-Null
resources MUST have defined values for lockdiscovery and
supportedlock properties.
Until a method such as PUT or MKCOL is successfully executed on the
lock-null resource the resource MUST stay in the lock-null state.
However, once a PUT or MKCOL is successfully executed on a lock-null
resource the resources ceases to be in the lock-null state.
If the resource is unlocked, for any reason, without a PUT, MKCOL,
or similar method having been successfully executed upon it then the
resource MUST return to the null state.
6.4 Write Locks and Collections
A write lock on a collection prevents the addition or removal of
members of the collection by non-lock owners. As a consequence,
when a principal issues a request to create a new internal member of
a write locked collection using PUT or POST, or to remove an
existing internal member of a write locked collection using DELETE,
this request MUST fail if the principal does not have a write lock
on the collection.
However, if a write lock request is issued to a collection
containing internal member resources that are currently locked in a
manner which conflicts with the write lock, the request MUST fail
with a 423 Locked status code.
If a lock owner causes a resource to be added as an internal member
of a locked collection then the new resource MUST be automatically
added to the lock. This is the only mechanism that allows a
Goland et al. [Page 18]
INTERNET-DRAFT WebDAV April 7, 1998
resource to be added to a write lock. Thus, for example, if the
collection /a/b/ is write locked and the resource /c is moved to
/a/b/c then /a/b/c will be added to the write lock.
6.5 Write Locks and the If Request Header
If a user agent is not required to have knowledge about a lock when
requesting an operation on a locked resource, the following scenario
might occur. Program A, run by User A, takes out a write lock on a
resource. Program B, also run by User A, has no knowledge of the
lock taken out by Program A, yet performs a PUT to the locked
resource. In this scenario, the PUT succeeds because locks are
associated with a principal, not a program, and thus program B,
because it is acting with principal A's credential, is allowed to
perform the PUT. However, had program B known about the lock, it
would not have overwritten the resource, preferring instead to
present a dialog box describing the conflict to the user. Due to
this scenario, a mechanism is needed to prevent different programs
from accidentally ignoring locks taken out by other programs with
the same authorization.
In order to prevent these collisions a lock token MUST be submitted
by an authorized principal in the If header for all locked resources
that a method may interact with or the method MUST fail. For
example, if a resource is to be moved and both the source and
destination are locked then two lock tokens must be submitted, one
for the source and the other for the destination.
6.5.1 Example - Write Lock
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
If:
()
>>Response
HTTP/1.1 204 No Content
In this example, even though both the source and destination are
locked, only one lock token must be submitted, for the lock on the
destination. This is because the source resource is not modified by
a COPY, and hence unaffected by the write lock. In this example,
user agent authentication has previously occurred via a mechanism
outside the scope of the HTTP protocol, in the underlying transport
layer.
Goland et al. [Page 19]
INTERNET-DRAFT WebDAV April 7, 1998
6.6 Write Locks and COPY/MOVE
A COPY method invocation MUST NOT duplicate any write locks active
on the source. However, as previously noted, if the COPY copies the
resource into a collection that is depth locked then the resource
will be added to the lock.
A MOVE MUST NOT move the write lock with the resource although the
resource is subject to being added to an existing lock as specified
in section 6.4. For example, if the MOVE makes the resource a child
of a collection that is depth locked then the resource will be under
that collection's lock. Additionally, if a depth locked resource is
moved to a destination that is within the scope of the same depth
lock (e.g., within the namespace tree covered by the lock), the
moved resource will again be a member of the lock. In both these
examples, as specified in section 6.5, an If header must be
submitted containing a lock token for both the source and
destination.
6.7 Refreshing Write Locks
A client MUST NOT submit the same write lock request twice. Note
that a client is always aware it is resubmitting the same lock
request because it must include the lock token in the If header in
order to make the request for a resource that is already locked.
However, a client may submit a LOCK method with an If header but
without a body. This form of LOCK MUST only be used to "refresh" a
lock. Meaning, at minimum, that any timers associated with the lock
MUST be re-set.
A server may return a Timeout header with a lock refresh that is
different than the Timeout header returned when the lock was
originally requested. Additionally clients may submit Timeout
headers of arbitrary value with their lock refresh requests.
Servers, as always, may ignore Timeout headers submitted by the
client.
If an error is received in response to a refresh LOCK request the
client SHOULD assume that the lock was not refreshed.
7 HTTP Methods for Distributed Authoring
The following new HTTP methods use XML as a request and response
format. All DAV compliant clients and resources MUST use XML
parsers that are compliant with [Bray, Paoli, Sperberg-McQueen,
1998]. All XML used in either requests or responses MUST be, at
minimum, well formed. If a server receives ill-formed XML in a
request it MUST reject the entire request with a 400 Bad Request.
If a client receives ill-formed XML in a response then it MUST NOT
assume anything about the outcome of the executed method and SHOULD
treat the server as malfunctioning.
Goland et al. [Page 20]
INTERNET-DRAFT WebDAV April 7, 1998
7.1 PROPFIND
The PROPFIND method retrieves properties defined on the Request-URI,
if the resource does not have any internal members, or on the
Request-URI and potentially its member resources, if the resource
does have internal members. All DAV compliant resources MUST
support the PROPFIND method and the propfind XML element (section
11.14) along with all XML elements defined for use with that
element.
A client may submit a Depth header with a value of "0", "1", or
"infinity" with a PROPFIND on a resource with internal members. DAV
compliant servers MUST support the "0", "1" and "infinity"
behaviors. By default, the PROPFIND method without a Depth header
MUST act as if a "Depth: infinity" header was included.
A client may submit a propfind XML element in the body of the
request method describing what information is being requested. It
is possible to request particular property values, all property
values, or a list of the names of the resource's properties. A
client may choose not to submit a request body. An empty PROPFIND
request body MUST be treated as a request for the names and values
of all properties.
All servers MUST support returning a response of content type
text/xml that contains a multistatus XML element that describes the
results of the attempts to retrieve the various properties.
If there is an error retrieving a property then a proper error
result MUST be included in the response. A request to retrieve the
value of a property which does not exist is an error and MUST be
noted, if the response uses a multistatus XML element, with a
response XML element which contains a 404 Not Found status value.
Consequently, the multistatus XML element for a resource with
members MUST include a response XML element for each member of the
resource, to whatever depth was requested. Each response XML element
MUST contain an href XML element that identifies the resource on
which the properties in the prop XML element are defined. Results
for a PROPFIND on a resource with internal members are returned as a
flat list whose order of entries is not significant.
In the case of allprop and propname, if a principal does not have
the right to know whether a particular property exists then the
property should be silently excluded from the response.
The results of this method SHOULD NOT be cached.
Goland et al. [Page 21]
INTERNET-DRAFT WebDAV April 7, 1998
7.1.1 Example - Retrieving Named Properties
>>Request
PROPFIND /file HTTP/1.1
Host: www.foo.bar
Content-type: text/xml
Content-Length: xyz
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxxx
http://www.foo.bar/fileBox type AJ.J. JohnsonHTTP/1.1 200 OKHTTP/1.1 403 Forbidden The user does not have access to
the DingALing property.
Goland et al. [Page 22]
INTERNET-DRAFT WebDAV April 7, 1998
There has been an access violation error.
In this example, PROPFIND is executed on a non-collection resource
http://www.foo.bar/file. The propfind XML element specifies the
name of four properties whose values are being requested. In this
case only two properties were returned, since the principal issuing
the request did not have sufficient access rights to see the third
and fourth properties.
7.1.2 Example - Using allprop to Retrieve All Properties
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Depth: 1
Content-Type: text/xml
Content-Length: xxxxx
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxxx
http://www.foo.bar/container/Box type AHadrian
1997-12-01T17:42:21-08:00
Example collection
Goland et al. [Page 23]
INTERNET-DRAFT WebDAV April 7, 1998
HTTP/1.1 200 OKhttp://www.foo.bar/container/front.htmlBox type B
1997-12-01T18:27:21-08:00
Example HTML resource
4525
text/html
zzyzx
Monday, 12-Jan-98 09:25:56 GMT
HTTP/1.1 200 OK
Goland et al. [Page 24]
INTERNET-DRAFT WebDAV April 7, 1998
In this example, PROPFIND was invoked on the resource
http://www.foo.bar/container/ with a Depth header of 1, meaning the
request applies to the resource and its children, and a propfind XML
element containing the allprop XML element, meaning the request
should return the name and value of all properties defined on each
resource.
The resource http://www.foo.bar/container/ has six properties
defined on it:
http://www.foo.bar/boxschema/bigbox,
http://www.foo.bar/boxschema/author, DAV:creationdate,
DAV:displayname, DAV:resourcetype, and DAV:supportedlock.
The last four properties are WebDAV-specific, defined in section 12.
Since GET is not supported on this resource, the get* properties
(e.g., getcontentlength) are not defined on this resource. The DAV-
specific properties assert that "container" was created on December
1, 1997, at 5:42:21PM, in a time zone 8 hours west of GMT
(creationdate), has a name of "Example collection" (displayname), a
collection resource type (resourcetype), and supports exclusive
write and shared write locks (supportedlock).
The resource http://www.foo.bar/container/front.html has nine
properties defined on it:
http://www.foo.bar/boxschema/bigbox (another instance of the
"bigbox" property type), DAV:creationdate, DAV:displayname,
DAV:getcontentlength, DAV:getcontenttype, DAV:getetag,
DAV:getlastmodified, DAV:resourcetype, and DAV:supportedlock.
The DAV-specific properties assert that "front.html" was created on
December 1, 1997, at 6:27:21PM, in a time zone 8 hours west of GMT
(creationdate), has a name of "Example HTML resource" (displayname),
a content length of 4525 bytes (getcontentlength), a MIME type of
"text/html" (getcontenttype), an entity tag of "zzyzx" (getetag),
was last modified on Monday, January 12, 1998, at 09:25:56 GMT
(getlastmodified), has an empty resource type, meaning that it is
not a collection (resourcetype), and supports both exclusive write
and shared write locks (supportedlock).
7.1.3 Example - Using propname to Retrieve all Property Names
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Content-Type: text/xml
Content-Length: xxxxx
Goland et al. [Page 25]
INTERNET-DRAFT WebDAV April 7, 1998
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxx
http://www.foo.bar/container/HTTP/1.1 200 OKhttp://www.foo.bar/container/front.htmlHTTP/1.1 200 OK
In this example, PROPFIND is invoked on the collection resource
http://www.foo.bar/container/, with a propfind XML element
Goland et al. [Page 26]
INTERNET-DRAFT WebDAV April 7, 1998
containing the propname XML element, meaning the name of all
properties should be returned. Since no depth header is present, it
assumes its default value of "infinity", meaning the name of the
properties on the collection and all its progeny should be returned.
Consistent with the previous example, resource
http://www.foo.bar/container/ has six properties defined on it,
http://www.foo.bar/boxschema/bigbox,
http://www.foo.bar/boxschema/author, DAV:creationdate,
DAV:displayname, DAV:resourcetype, and DAV:supportedlock.
The resource http://www.foo.bar/container/index.html, a member of
the "container" collection, has nine properties defined on it,
http://www.foo.bar/boxschema/bigbox, DAV:creationdate,
DAV:displayname, DAV:getcontentlength, DAV:getcontenttype,
DAV:getetag, DAV:getlastmodified, DAV:resourcetype, and
DAV:supportedlock.
7.2 PROPPATCH
The PROPPATCH method processes instructions specified in the request
body to set and/or remove properties defined on the resource
identified by the Request-URI.
All DAV compliant resources MUST support the PROPPATCH method and
MUST process instructions that are specified using the
propertyupdate, set, and remove XML elements of the DAV schema.
Execution of the directives in this method is, of course, subject to
access control constraints. DAV compliant resources SHOULD support
the setting of arbitrary dead properties.
The request message body of a PROPPATCH method MUST contain the
propertyupdate XML element. Instruction processing MUST occur in
the order instructions are received (i.e., from top to bottom).
Instructions MUST either all be executed or none executed. Thus if
any error occurs during processing all executed instructions MUST be
undone and a proper error result returned. Instruction processing
details can be found in the definition of the set and remove
instructions in section 11.13.
7.2.1 Status Codes for use with Multi-Status
The following are examples of response codes one would expect to be
used in a Multi-Status response for this method. Note, however,
that unless explicitly prohibited any 2/3/4/5xx series response code
may be used in a Multi-Status response.
200 OK - The command succeeded. As there can be a mixture of sets
and removes in a body, a 201 Created seems inappropriate.
403 Forbidden - The client, for reasons the server chooses not to
specify, cannot alter one of the properties.
Goland et al. [Page 27]
INTERNET-DRAFT WebDAV April 7, 1998
409 Conflict - The client has provided a value whose semantics are
not appropriate for the property. This includes trying to set read-
only properties.
423 Locked - The specified resource is locked and the client either
is not a lock owner or the lock type requires a lock token to be
submitted and the client did not submit it.
425 Insufficient Space on Resource - The server did not have
sufficient space to record the property.
7.2.2 Example - PROPPATCH
>>Request
PROPPATCH /bar.html HTTP/1.1
Host: www.foo.com
Content-Type: text/xml
Content-Length: xxxx
Jim WhiteheadRoy Fielding
Goland et al. [Page 28]
INTERNET-DRAFT WebDAV April 7, 1998
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxxx
http://www.foo.com/bar.htmlHTTP/1.1 424 Method FailureHTTP/1.1 409 Conflict Copyright Owner can not be deleted or
altered.
In this example, the client requests the server to set the value of
the http://www.w3.com/standards/z39.50/Authors property, and to
remove the property http://www.w3.com/standards/z39.50/Copyright-
Owner. Since the Copyright-Owner property could not be removed, no
property modifications occur. The Method Failure status code for
the Authors property indicates this action would have succeeded if
it were not for the conflict with removing the Copyright-Owner
property.
7.3 MKCOL Method
The MKCOL method is used to create a new collection. All DAV
compliant resources MUST support the MKCOL method.
7.3.1 Request
MKCOL creates a new collection resource at the location specified by
the Request-URI. If the resource identified by the Request-URI is
non-null then the MKCOL MUST fail. During MKCOL processing, a
server MUST make the Request-URI a member of its parent collection,
unless the Request-URI is "/". If no such ancestor exists, the
method MUST fail. When the MKCOL operation creates a new collection
resource, all ancestors MUST already exist, or the method MUST fail
with a 409 Conflict status code. For example, if a request to
create collection /a/b/c/d/ is made, and neither /a/b/ nor /a/b/c/
exists, the request must fail.
Goland et al. [Page 29]
INTERNET-DRAFT WebDAV April 7, 1998
When MKCOL is invoked without a request body, the newly created
collection SHOULD have no members.
A MKCOL request message may contain a message body. The behavior of
a MKCOL request when the body is present is limited to creating
collections, members of a collection, bodies of members and
properties on the collections or members. If the server receives a
MKCOL request entity type it does not support or understand it MUST
respond with a 415 Unsupported Media Type status code. The exact
behavior of MKCOL for various request media types is undefined in
this document, and will be specified in separate documents.
7.3.2 Response Codes
Responses from a MKCOL request MUST NOT be cached as MKCOL has non-
idempotent semantics.
201 Created - The collection or structured resource was created in
its entirety.
403 Forbidden - This indicates at least one of two conditions: 1)
the server does not allow the creation of collections at the given
location in its namespace, or 2) the parent collection of the
Request-URI exists but cannot accept members.
405 Method Not Allowed - MKCOL can only be executed on a
deleted/non-existent resource.
409 Conflict - A collection cannot be made at the Request-URI until
one or more intermediate collections have been created.
415 Unsupported Media Type- The server does not support the request
type of the body.
425 Insufficient Space on Resource - The resource does not have
sufficient space to record the state of the resource after the
execution of this method.
7.3.3 Example - MKCOL
This example creates a collection called /webdisc/xfiles/ on the
server www.server.org.
>>Request
MKCOL /webdisc/xfiles/ HTTP/1.1
Host: www.server.org
>>Response
HTTP/1.1 201 Created
Goland et al. [Page 30]
INTERNET-DRAFT WebDAV April 7, 1998
7.4 GET, HEAD for Collections
The semantics of GET are unchanged when applied to a collection,
since GET is defined as, "retrieve whatever information (in the form
of an entity) is identified by the Request-URI" [Fielding et al.,
1997]. GET when applied to a collection may return the contents of
an "index.html" resource, a human-readable view of the contents of
the collection, or something else altogether. Hence it is possible
that the result of a GET on a collection will bear no correlation to
the membership of the collection.
Similarly, since the definition of HEAD is a GET without a response
message body, the semantics of HEAD are unmodified when applied to
collection resources.
7.5 POST for Collections
Since by definition the actual function performed by POST is
determined by the server and often depends on the particular
resource, the behavior of POST when applied to collections cannot be
meaningfully modified because it is largely undefined. Thus the
semantics of POST are unmodified when applied to a collection.
7.6 DELETE
7.6.1 DELETE for Non-Collection Resources
If the DELETE method is issued to a non-collection resource which is
an internal member of a collection, then during DELETE processing a
server MUST remove the Request-URI from its parent collection.
7.6.2 DELETE for Collections
The DELETE method on a collection MUST act as if a "Depth: infinity"
header was used on it. A client MUST NOT submit a Depth header with
a DELETE on a collection with any value but infinity.
DELETE instructs that the collection specified in the request-URI
and all its internal member resources are to be deleted.
If any member cannot be deleted then all of the member's ancestors
MUST NOT be deleted, so as to maintain the namespace.
Any headers included with DELETE MUST be applied in processing every
resource to be deleted.
When the DELETE method has completed processing it MUST return a
consistent namespace.
Goland et al. [Page 31]
INTERNET-DRAFT WebDAV April 7, 1998
If an error occurs with a resource other than the resource
identified in the request URI then the response MUST be a 207 Multi-
Status. 424 Method Failure errors SHOULD NOT be in the 207 Multi-
Status. They can be safely left out because the client will know
that the ancestors of a resource could not be deleted when the
client receives an error for the ancestor's progeny. Additionally
204 No Content errors SHOULD NOT be returned in the 207 Multi-
Status. The reason for this prohibition is that 204 No Content is
the default success code.
7.6.2.1 Example - DELETE
>>Request
DELETE /container/ HTTP/1.1
Host: www.foo.bar
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxxx
http://www.foo.bar/container/resource3HTTP/1.1 423 Locked
In this example the attempt to delete
http://www.foo.bar/container/resource3 failed because it is locked,
and no lock token was submitted with the request. Consequently, the
attempt to delete http://www.foo.bar/container/ also failed. Thus
the client knows that the attempt to delete
http://www.foo.bar/container/ must have also failed since the parent
can not be deleted unless its child has also been deleted. Even
though a Depth header has not been included, a depth of infinity is
assumed because the method is on a collection.
7.7 PUT
7.7.1 PUT for Non-Collection Resources
A PUT performed on an existing resource replaces the GET response
entity of the resource. Properties defined on the resource may be
recomputed during PUT processing but are not otherwise affected.
For example, if a server recognizes the content type of the request
body, it may be able to automatically extract information that could
be profitably exposed as properties.
Goland et al. [Page 32]
INTERNET-DRAFT WebDAV April 7, 1998
A PUT that would result in the creation of a resource without an
appropriately scoped parent collection MUST fail with a 409
Conflict.
7.7.2 PUT for Collections
As defined in the HTTP/1.1 specification [Fielding et al., 1997],
the "PUT method requests that the enclosed entity be stored under
the supplied Request-URI." Since submission of an entity
representing a collection would implicitly encode creation and
deletion of resources, this specification intentionally does not
define a transmission format for creating a collection using PUT.
Instead, the MKCOL method is defined to create collections.
When the PUT operation creates a new non-collection resource all
ancestors MUST already exist. If all ancestors do not exist, the
method MUST fail with a 409 Conflict status code. For example, if
resource /a/b/c/d.html is to be created and /a/b/c/ does not exist,
then the request must fail.
7.8 COPY Method
The COPY method creates a duplicate of the source resource, given by
the Request-URI, in the destination resource, given by the
Destination header. The Destination header MUST be present. The
exact behavior of the COPY method depends on the type of the source
resource.
All WebDAV compliant resources MUST support the COPY method.
However, support for the COPY method does not guarantee the ability
to copy a resource. For example, separate programs may control
resources on the same server. As a result, it may not be possible
to copy a resource to a location that appears to be on the same
server.
7.8.1 COPY for HTTP/1.1 resources
When the source resource is not a collection the result of the COPY
method is the creation of a new resource at the destination whose
state and behavior match that of the source resource as closely as
possible. However, the exact state and behavior of the destination
resource depend on what information the source resource is able to
provide and what information the destination resource is able to
accept.
Subsequent alterations to the destination resource will not modify
the source resource. Subsequent alterations to the source resource
will not modify the destination resource.
Goland et al. [Page 33]
INTERNET-DRAFT WebDAV April 7, 1998
All properties on the source resource MUST be duplicated on the
destination resource, subject to modifying headers and XML elements,
following the definition for copying properties.
7.8.2 COPY for Properties
The following section defines how properties on a resource are
handled during a COPY operation.
Live properties SHOULD be duplicated as identically behaving live
properties at the destination resource. If a property cannot be
copied live, then its value MUST be duplicated, octet-for-octet, in
an identically named, dead property on the destination resource
subject to the effects of the propertybehavior XML element.
The propertybehavior XML element can specify that properties are
copied on best effort, that all live properties must be successfully
copied or the method must fail, or that a specified list of live
properties must be successfully copied or the method must fail. The
propertybehavior XML element is defined in section 11.12.
7.8.3 COPY for Collections
The COPY method on a collection without a Depth header MUST act as
if a Depth header with value "infinity" was included. A client may
submit a Depth header on a COPY on a collection with a value of "0"
or "infinity". DAV compliant servers MUST support the "0" and
"infinity" Depth header behaviors.
A COPY of depth infinity instructs that the collection specified in
the Request-URI is to be copied to the location specified in the
Destination header, and all its internal member resources are to be
copied to a location relative to it, recursively through all levels
of the collection hierarchy.
A COPY of depth "0" only instructs that the collection and its
properties but not its internal members, are to be copied.
Any headers included with a COPY MUST be applied in processing every
resource to be copied with the exception of the Destination header.
The Destination header only specifies the destination for the
Request-URI. When applied to members of the collection specified in
the request-URI the value of Destination is to be modified to
reflect the current location in the hierarchy. So, if the request-
URI is /a/ and the destination is /b/ then when /a/c/d is processed
it must use a destination of /b/c/d.
When the COPY method has completed processing it MUST have created a
consistent namespace at the destination. However, if an error
occurs while copying an internal member collection, the server MUST
NOT copy any members of this collection. After detecting an error,
Goland et al. [Page 34]
INTERNET-DRAFT WebDAV April 7, 1998
the COPY operation SHOULD try to finish as much of the original copy
operation as possible. So, for example, if an infinite depth copy
operation is performed on collection /a/, which contains collections
/a/b/ and /a/c/, and an error occurs copying /a/b/, an attempt
should still be made to copy /a/c/. Similarly, after encountering an
error copying a non-collection resource as part of an infinite depth
copy, the server SHOULD try to finish as much of the original copy
operation as possible.
If an error in executing the COPY method occurs with a resource
other than the resource identified in the request URI then the
response MUST be a 207 Multi-Status.
424 Method Failure errors SHOULD NOT be returned in the 207 Multi-
Status from a COPY method. These responses can be safely omitted
because the client will know that the progeny of a resource could
not be copied when the client receives an error for the parent.
Additionally 201 Created/204 No Content response codes SHOULD NOT be
returned as values in 207 Multi-Status responses from COPY methods.
They, too, can be safely omitted because they are the default
success codes.
7.8.4 COPY and the Overwrite Header
If a resource exists at the destination and the Overwrite header is
"T" then prior to performing the copy the server MUST perform a
DELETE with Depth Infinity on the destination resource. If the
Overwrite header is set to "F" then the operation will fail.
7.8.5 Status Codes
201 Created - The source resource was successfully copied. The copy
operation resulted in the creation of a new resource.
204 No Content - The source resource was successfully copied to a
pre-existing destination resource.
412 Precondition Failed - The server was unable to maintain the
liveness of the properties listed in the propertybehavior XML
element or the Overwrite header is "F" and the state of the
destination resource is non-null.
423 Locked - The destination resource was locked.
425 Insufficient Space on Resource - The destination resource does
not have sufficient space to record the state of the resource after
the execution of this method.
502 Bad Gateway - This may occur when the destination is on another
server and the destination server refuses to accept the resource.
Goland et al. [Page 35]
INTERNET-DRAFT WebDAV April 7, 1998
7.8.6 Example - COPY with Overwrite
This example shows resource
http://www.ics.uci.edu/~fielding/index.html being copied to the
location http://www.ics.uci.edu/users/f/fielding/index.html. The
204 No Content status code indicates the existing resource at the
destination was overwritten.
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
>>Response
HTTP/1.1 204 No Content
7.8.7 Example - COPY with No Overwrite
The following example shows the same copy operation being performed,
but with the Overwrite header set to "F." A response of 412
Precondition Failed is returned because the destination resource has
a non-null state.
>>Request
COPY /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
Overwrite: F
>>Response
HTTP/1.1 412 Precondition Failed
7.8.8 Example - COPY of a Collection
>>Request
COPY /container/ HTTP/1.1
Host: www.foo.bar
Destination: http://www.foo.bar/othercontainer/
Depth: infinity
Content-Type: text/xml
Content-Length: xxxxx
*
Goland et al. [Page 36]
INTERNET-DRAFT WebDAV April 7, 1998
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxxx
http://www.foo.bar/othercontainer/R2/HTTP/1.1 412 Precondition Failed
The Depth header is unnecessary as the default behavior of COPY on a
collection is to act as if a "Depth: infinity" header had been
submitted. In this example most of the resources, along with the
collection, were copied successfully. However the collection R2
failed, most likely due to a problem with maintaining the liveness
of properties (this is specified by the propertybehavior XML
element). Because there was an error copying R2, none of R2's
members were copied. However no errors were listed for those
members due to the error minimization rules given in section 7.8.3.
7.9 MOVE Method
The MOVE operation on a non-collection resource is the logical
equivalent of a copy (COPY) followed by a delete of the source,
where the actions are performed atomically. Consequently, the
Destination header MUST be present on all MOVE methods and MUST
follow all COPY requirements for the COPY part of the MOVE method.
All DAV compliant resources MUST support the MOVE method. However,
support for the MOVE method does not guarantee the ability to move a
resource to a particular destination.
For example, separate programs may actually control different sets
of resources on the same server. Therefore, it may not be possible
to move a resource within a namespace that appears to belong to the
same server.
If a resource exists at the destination, the destination resource
will be DELETEd as a side-effect of the MOVE operation, subject to
the restrictions of the Overwrite header.
7.9.1 MOVE for Properties
The behavior of properties on a MOVE, including the effects of the
propertybehavior XML element, MUST be the same as specified in
section 7.8.2.
Goland et al. [Page 37]
INTERNET-DRAFT WebDAV April 7, 1998
7.9.2 MOVE for Collections
A MOVE of depth infinity instructs that the collection specified in
the Request-URI be moved to the location specified in the
Destination header, and all its internal member resources are to be
moved to locations relative to it, recursively through all levels of
the collection hierarchy.
The MOVE method on a collection MUST act as if a Depth "infinity"
header was used on it. A client MUST NOT submit a Depth header on a
MOVE on a collection with any value but "infinity".
Any headers included with MOVE MUST be applied in processing every
resource to be moved with the exception of the Destination header.
The behavior of the Destination header is the same as given for COPY
on collections.
When the MOVE method has completed processing it MUST have created a
consistent namespace on both the source and destination. However, if
an error occurs while moving an internal member collection, the
server MUST NOT move any members of the failed collection.. In this
case, after detecting the error, the move operation SHOULD try to
finish as much of the original move as possible. So, for example,
if an infinite depth move is performed on collection /a/, which
contains collections /a/b/ and /a/c/, and an error occurs moving
/a/b/, an attempt should still be made to try moving /a/c/.
Similarly, after encountering an error moving a non-collection
resource as part of an infinite depth move, the server SHOULD try to
finish as much of the original move operation as possible.
If an error occurs with a resource other than the resource
identified in the request URI then the response MUST be a 207 Multi-
Status.
424 Method Failure errors SHOULD NOT be returned as values in the
207 Multi-Status from a MOVE method. These errors can be safely
omitted because the client will know that the progeny of a resource
could not be moved when the client receives an error for the parent.
Additionally 201 Created/204 No Content responses SHOULD NOT be
returned as values in 207 Multi-Status responses from MOVES. These
responses can be safely omitted because they are the default success
codes.
7.9.3 MOVE and the Overwrite Header
If a resource exists at the destination and the Overwrite header is
"T" then prior to performing the move the server MUST perform a
DELETE with Depth infinity on the destination resource. If the
Overwrite header is set to "F" then the operation will fail.
Goland et al. [Page 38]
INTERNET-DRAFT WebDAV April 7, 1998
7.9.4 Status Codes
201 Created - The source resource was successfully moved, and a new
resource was created at the destination.
204 No Content - The source resource was successfully moved to a
pre-existing destination resource.
412 Precondition Failed - The server was unable to maintain the
liveness of the properties listed in the propertybehavior XML
element or the Overwrite header is "F" and the state of the
destination resource is non-null.
423 Locked - The source or the destination resource was locked.
502 Bad Gateway - This may occur when the destination is on another
server and the destination server refuses to accept the resource.
7.9.5 Example - MOVE of a Non-Collection
This example shows resource
http://www.ics.uci.edu/~fielding/index.html being moved to the
location http://www.ics.uci.edu/users/f/fielding/index.html. The
contents of the destination resource would have been overwritten if
the destination resource had been non-null. In this case, since
there was nothing at the destination resource, the response code is
201 Created.
>>Request
MOVE /~fielding/index.html HTTP/1.1
Host: www.ics.uci.edu
Destination: http://www.ics.uci.edu/users/f/fielding/index.html
>>Response
HTTP/1.1 201 Created
Content-Location: http://www.ics.uci.edu/users/f/fielding/index.html
7.9.6 Example - MOVE of a Collection
>>Request
MOVE /container/ HTTP/1.1
Host: www.foo.bar
Destination: http://www.foo.bar/othercontainer/
Overwrite: F
If: ()
()
Content-Type: text/xml
Goland et al. [Page 39]
INTERNET-DRAFT WebDAV April 7, 1998
Content-Length: xyz
*
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: zzz
http://www.foo.bar/othercontainer/C2/HTTP/1.1 423 Locked
In this example the client has submitted a number of lock tokens
with the request. A lock token will need to be submitted for every
resource, both source and destination, anywhere in the scope of the
method, that is locked. In this case the proper lock token was not
submitted for the destination http://www.foo.bar/othercontainer/C2/.
This means that the resource /container/C2/ could not be moved.
Because there was an error copying /container/C2/, none of
/container/C2's members were copied. However no errors were listed
for those members due to the error minimization rules given in
section 7.8.3. User agent authentication has previously occurred
via a mechanism outside the scope of the HTTP protocol, in an
underlying transport layer.
7.10 LOCK Method
The following sections describe the LOCK method, which is used to
take out a lock of any access type. These sections on the LOCK
method describe only those semantics that are specific to the LOCK
method and are independent of the access type of the lock being
requested.
Any resource which supports the LOCK method MUST, at minimum,
support the XML request and response formats defined herein.
7.10.1 Operation
A LOCK method invocation creates the lock specified by the lockinfo
XML element on the Request-URI. Lock method requests SHOULD have a
XML request body which contains an owner XML element for this lock
Goland et al. [Page 40]
INTERNET-DRAFT WebDAV April 7, 1998
request, unless this is a refresh request. The LOCK request may have
a Timeout header.
Clients MUST assume that locks may arbitrarily disappear at any
time, regardless of the value given in the Timeout header. The
Timeout header only indicates the behavior of the server if
"extraordinary" circumstances do not occur. For example, an
administrator may remove a lock at any time or the system may crash
in such a way that it loses the record of the lock's existence. The
response MUST contain the value of the lockdiscovery property in a
prop XML element.
7.10.2 The Effect of Locks on Properties and Collections
The scope of a lock is the entire state of the resource, including
its body and associated properties. As a result, a lock on a
resource MUST also lock the resource's properties.
For collections, a lock also affects the ability to add or remove
members. The nature of the effect depends upon the type of access
control involved.
7.10.3 Locking Replicated Resources
Some servers automatically replicate resources across multiple URLs.
In such a circumstance the server MUST only accept a lock on one of
the URLs if the server can guarantee that the lock will be honored
across all the URLs.
7.10.4 Depth and Locking
The Depth header may be used with the LOCK method. Values other
than 0 or infinity MUST NOT be used with the Depth header on a LOCK
method. All resources that support the LOCK method MUST support the
Depth header.
A Depth header of value 0 means to just lock the resource specified
by the request-URI.
If the Depth header is set to infinity then the resource specified
in the request-URI along with all its internal members, all the way
down the hierarchy, are to be locked. A successful result MUST
return a single lock token which represents all the resources that
have been locked. If an UNLOCK is successfully executed on this
token, all associated resources are unlocked. If the lock cannot be
granted to all resources, a 409 Conflict status code MUST be
returned with a response entity body containing a multistatus XML
element describing which resource(s) prevented the lock from being
granted. Hence, partial success is not an option. Either the
entire hierarchy is locked or no resources are locked.
Goland et al. [Page 41]
INTERNET-DRAFT WebDAV April 7, 1998
If no depth header is submitted on a LOCK request then the request
MUST act as if a Depth of infinity had been submitted.
7.10.5 Interaction with other Methods
The interaction of a LOCK with various methods is dependent upon the
lock type. However, independent of lock type, a successful DELETE
of a resource MUST cause all of its locks to be removed.
7.10.6 Lock Compatibility Table
The table below describes the behavior that occurs when a lock
request is made on a resource.
Current lock state/ Shared Lock Exclusive
Lock request Lock
None True True
Shared Lock True False
Exclusive Lock False False*
Legend: True = lock may be granted. False = lock MUST NOT be
granted. *=It is illegal for a principal to request the same lock
twice.
The current lock state of a resource is given in the leftmost
column, and lock requests are listed in the first row. The
intersection of a row and column gives the result of a lock request.
For example, if a shared lock is held on a resource, and an
exclusive lock is requested, the table entry is "false", indicating
the lock must not be granted.
7.10.7 Status Codes
200 Success - The lock request succeeded and the value of the
lockdiscovery property is included in the body.
412 Precondition Failed - The included lock token was not
enforceable on this resource or the server could not satisfy the
request in the lockinfo XML element.
423 Locked - The resource is locked, so the method has been
rejected.
Goland et al. [Page 42]
INTERNET-DRAFT WebDAV April 7, 1998
7.10.8 Example - Simple Lock Request
>>Request
LOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: webdav.sb.aol.com
Timeout: Infinite, Second-4100000000
Content-Type: text/xml
Content-Length: xyz
Authorization: Digest username="ejw",
realm="ejw@webdav.sb.aol.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
http://www.ics.uci.edu/~ejw/contact.html
>>Response
HTTP/1.1 200 OK
Content-Type: text/xml
Content-Length: xxxxx
Infinity
http://www.ics.uci.edu/~ejw/contact.html
Second-604800
opaquelocktoken:e71d4fae-5dec-22d6-fea5-00a0c91e6be4
Goland et al. [Page 43]
INTERNET-DRAFT WebDAV April 7, 1998
This example shows the successful creation of an exclusive write
lock on resource
http://webdav.sb.aol.com/workspace/webdav/proposal.doc. The
resource http://www.ics.uci.edu/~ejw/contact.html contains contact
information for the owner of the lock. The server has an activity-
based timeout policy in place on this resource, which causes the
lock to automatically be removed after 1 week (604800 seconds).
Note that the nonce, response, and opaque fields have not been
calculated in the Authorization request header.
7.10.9 Example - Refreshing a Write Lock
>>Request
LOCK /workspace/webdav/proposal.doc HTTP/1.1
Host: webdav.sb.aol.com
Timeout: Infinite, Second-4100000000
If: ()
Authorization: Digest username="ejw",
realm="ejw@webdav.sb.aol.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
>>Response
HTTP/1.1 200 OK
Content-Type: text/xml
Content-Length: xxxxx
Infinity
http://www.ics.uci.edu/~ejw/contact.html
Second-604800
opaquelocktoken:e71d4fae-5dec-22d6-fea5-00a0c91e6be4
Goland et al. [Page 44]
INTERNET-DRAFT WebDAV April 7, 1998
This request would refresh the lock, resetting any time outs.
Notice that the client asked for an infinite time out but the server
choose to ignore the request. In this example, the nonce, response,
and opaque fields have not been calculated in the Authorization
request header.
7.10.10 Example - Multi-Resource Lock Request
>>Request
LOCK /webdav/ HTTP/1.1
Host: webdav.sb.aol.com
Timeout: Infinite, Second-4100000000
Depth: infinity
Authorization: Digest username="ejw",
realm="ejw@webdav.sb.aol.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
http://www.ics.uci.edu/~ejw/contact.html
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxxx
http://webdav.sb.aol.com/webdav/secretHTTP/1.1 403 Forbiddenhttp://webdav.sb.aol.com/webdav/HTTP/1.1 424 Method Failure
Goland et al. [Page 45]
INTERNET-DRAFT WebDAV April 7, 1998
This example shows a request for an exclusive write lock on a
collection and all its children. In this request, the client has
specified that it desires an infinite length lock, if available,
otherwise a timeout of 4.1 billion seconds, if available. The
request entity body contains the contact information for the
principal taking out the lock, in this case a web page URL.
The error is a 403 Forbidden response on the resource
http://webdav.sb.aol.com/webdav/secret. Because this resource could
not be locked, none of the resources were locked. Note also that
the lockdiscovery property for the Request-URI has been included as
required. In this example the lockdiscovery property is empty which
means that there are no outstanding locks on the resource.
In this example, the nonce, response, and opaque fields have not
been calculated in the Authorization request header.
7.11 UNLOCK Method
The UNLOCK method removes the lock identified by the lock token in
the Lock-Token request header from the Request-URI, and all other
resources included in the lock. If all resources which have been
locked under the submitted lock token can not be unlocked then the
UNLOCK request MUST fail.
Any DAV compliant resource which supports the LOCK method MUST
support the UNLOCK method.
7.11.1 Example - UNLOCK
>>Request
UNLOCK /workspace/webdav/info.doc HTTP/1.1
Host: webdav.sb.aol.com
Lock-Token:
Authorization: Digest username="ejw",
realm="ejw@webdav.sb.aol.com", nonce="...",
uri="/workspace/webdav/proposal.doc",
response="...", opaque="..."
>>Response
HTTP/1.1 204 No Content
In this example, the lock identified by the lock token
"opaquelocktoken:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7" is
successfully removed from the resource
http://webdav.sb.aol.com/workspace/webdav/info.doc. If this lock
included more than just one resource, the lock is removed from all
resources included in the lock. The 204 status code is used instead
of 200 OK because there is no response entity body.
Goland et al. [Page 46]
INTERNET-DRAFT WebDAV April 7, 1998
In this example, the nonce, response, and opaque fields have not
been calculated in the Authorization request header.
8 HTTP Headers for Distributed Authoring
8.1 DAV Header
DAV = "DAV" ":" "1" ["," "2"] ["," 1#extend]
This header indicates that the resource supports the DAV schema and
protocol as specified. All DAV compliant resources MUST return the
DAV header on all OPTIONS responses.
The value is a list of all compliance classes that the resource
supports. Note that above a comma has already been added to the 2.
This is because a resource can not be level 2 compliant unless it is
also level 1 compliant. Please refer to section 14 for more details.
In general, however, support for one compliance class does not
entail support for any other.
8.2 Depth Header
Depth = "Depth" ":" ("0" | "1" | "infinity")
The Depth header is used with methods executed on resources which
could potentially have internal members to indicate whether the
method is to be applied only to the resource (Depth = 0), to the
resource and its immediate children, (Depth = 1), or the resource
and all its progeny (Depth = infinity).
The Depth header is only supported if a method's definition
explicitly provides for such support.
The following rules are the default behavior for any method that
supports the Depth header. A method may override these defaults by
defining different behavior in its definition.
Methods which support the Depth header may choose not to support all
of the header's values and may define, on a case by case basis, the
behavior of the method if a Depth header is not present. For
example, the MOVE method only supports Depth = infinity and if a
Depth header is not present will act as if a Depth = infinity header
had been applied.
Clients MUST NOT rely upon methods executing on members of their
hierarchies in any particular order or on the execution being atomic
unless the particular method explicitly provides such guarantees.
Upon execution, a method with a Depth header will perform as much of
its assigned task as possible and then return a response specifying
what it was able to accomplish and what it failed to do.
Goland et al. [Page 47]
INTERNET-DRAFT WebDAV April 7, 1998
So, for example, an attempt to COPY a hierarchy may result in some
of the members being copied and some not.
Any headers on a method that has a defined interaction with the
Depth header MUST be applied to all resources in the scope of the
method except where alternative behavior is explicitly defined. For
example, an If-Match header will have its value applied against
every resource in the method's scope and will cause the method to
fail if the header fails to match.
If a resource, source or destination, within the scope of the method
with a depth header is locked in such a way as to prevent the
successful execution of the method, then the lock token for that
resource MUST be submitted with the request in the If request
header.
The Depth header only specifies the behavior of the method with
regards to internal children. If a resource does not have internal
children then the Depth header MUST be ignored.
Please note, however, that it is always an error to submit a value
for the Depth header that is not allowed by the method's definition.
Thus submitting a "Depth: 1" on a COPY, even if the resource does
not have internal members, will result in a 400 Bad Request. The
method should fail not because the resource doesn't have internal
members, but because of the illegal value in the header.
8.3 Destination Header
Destination = "Destination" ":" URI
The Destination header specifies a destination resource for methods
such as COPY and MOVE, which take two URIs as parameters.
8.4 If Header
If = "If" ":" ( 1*No-tag-list | 1*Tagged-list)
No-tag-list = List
Tagged-list = Resource 1*List
Resource = Coded-url
List = "(" 1*(["Not"](State-token | "[" entity-tag "]")) ")"
State-token = Coded-url
Coded-url = ""
The If header is intended to have similar functionality to the If-
Match header defined in section 14.25 of [Fielding et al., 1997].
However the If header is intended for use with any URI which
represents state information, referred to as a state token, about a
resource as well as e-tags. A typical example of a state token is a
lock token, and lock tokens are the only state tokens defined in
this specification.
Goland et al. [Page 48]
INTERNET-DRAFT WebDAV April 7, 1998
All DAV compliant resources MUST honor the If header.
The If header's purpose is to describe a series of state lists. If
the state of the resource to which the header is applied does not
match any of the specified state lists then the request MUST fail
with a 412 Precondition Failed. If one of the described state lists
matches the state of the resource then the request may succeed.
8.4.1 No-tag-list Production
The No-tag-list production describes a series of state tokens and e-
tags. If multiple No-tag-list productions are used then only one
needs to match the state of the resource for the method to be
allowed to continue.
If a method, due to the presence of a Depth or Destination header,
is applied to multiple resources then the No-tag-list production
MUST be applied to each resource the method is applied to.
8.4.1.1 Example - No-tag-list If Header
If: ( ["I am an e-tag"]) (["I am
another e-tag"])
The previous header would require that any resources within the
scope of the method must either be locked with the specified lock
token and in the state identified by the "I am an e-tag" e-tag or in
the state identified by the second e-tag "I am another e-tag". To
put the matter more plainly one can think of the previous If header
as being in the form (or (and ["I am
an e-tag"]) (and ["I am another e-tag"])).
8.4.2 Tagged-list Production
The tagged-list production scopes a list production. That is, it
specifies that the lists following the resource specification only
apply to the specified resource. The scope of the resource
production begins with the list production immediately following the
resource production and ends with the next resource production, if
any.
When the If header is applied to a particular resource, the Tagged-
list productions MUST be searched to determine if any of the listed
resources match the operand resource(s) for the current method. If
none of the resource productions match the current resource then the
header MUST be ignored. If one of the resource productions does
match the name of the resource under consideration then the list
productions following the resource production MUST be applied to the
resource in the manner specified in the previous section.
Goland et al. [Page 49]
INTERNET-DRAFT WebDAV April 7, 1998
The same URI MUST NOT appear more than once in a resource production
in an If header.
8.4.2.1 Example - Tagged List If header
COPY /resource1 HTTP/1.1
Host: www.foo.bar
Destination: http://www.foo.bar/resource2
If: (
[W/"A weak e-tag"]) (["strong e-tag"])
(["another strong e-tag"])
In this example http://www.foo.bar/resource1 is being copied to
http://www.foo.bar/resource2. When the method is first applied to
http://www.foo.bar/resource1, resource1 must be in the state
specified by "( [W/"A weak e-tag"])
(["strong e-tag"])", that is, it either must be locked with a lock
token of "locktoken:a-write-lock-token" and have a weak entity tag
W/"A weak e-tag" or it must have a strong entity tag "strong e-tag".
That is the only success condition since the resource
http://www.bar.bar/random never has the method applied to it (the
only other resource listed in the If header) and
http://www.foo.bar/resource2 is not listed in the If header.
8.4.3 not Production
Every state token or e-tag is either current, and hence describes
the state of a resource, or is not current, and does not describe
the state of a resource. The boolean operation of matching a state
token or e-tag to the current state of a resource thus resolves to a
true or false value. The not production is used to reverse that
value. The scope of the not production is the state-token or
entity-tag immediately following it.
If: (Not )
When submitted with a request, this If header requires that all
operand resources must not be locked with locktoken:write1 and must
be locked with locktoken:write2.
8.4.4 Matching Function
When performing If header processing, the definition of a matching
state token or entity tag is as follows.
Matching entity tag: Where the entity tag matches an entity tag
associated with that resource.
Matching state token: Where there is an exact match between the
state token in the If header and any state token on the resource.
Goland et al. [Page 50]
INTERNET-DRAFT WebDAV April 7, 1998
8.4.5 If Header and Non-DAV Compliant Proxies
Non-DAV compliant proxies will not honor the If header, since they
will not understand the If header, and HTTP requires non-understood
headers to be ignored. When communicating with HTTP/1.1 proxies,
the "Cache-Control: no-cache" request header MUST be used so as to
prevent the proxy from improperly trying to service the request from
its cache. When dealing with HTTP/1.0 proxies the "Pragma: no-
cache" request header MUST be used for the same reason.
8.5 Lock-Token Request Header
Lock-Token = "Lock-Token" ":" Coded-URL
The Lock-Token request header is used with the UNLOCK method to
identify the lock to be removed. The lock token in the Lock-Token
request header MUST identify a lock that contains the resource
identified by Request-URI as a member.
8.6 Overwrite Header
Overwrite = "Overwrite" ":" ("T" | "F")
The Overwrite header specifies whether the server should overwrite
the state of a non-null destination resource during a COPY or MOVE.
A value of "F" states that the server must not perform the COPY or
MOVE operation if the state of the destination resource is non-null.
If the overwrite header is not included in a COPY or MOVE request
then the resource MUST treat the request as if it has an overwrite
header of value "T". While the Overwrite header appears to duplicate
the functionality of the If-Match: * header of HTTP/1.1, If-Match
applies only to the Request-URI, and not to the Destination of a
COPY or MOVE.
If a COPY or MOVE is not performed due to the value of the Overwrite
header, the method MUST fail with a 409 Conflict status code.
All DAV compliant resources MUST support the Overwrite header.
8.7 Status-URI Response Header
The Status-URI response header may be used with the 102 Processing
status code to inform the client as to the status of a method.
Status-URI = "Status-URI" ":" *(Status-Code "") ; Status-
Code is defined in 6.1.1 of [Fielding et al., 1997]
The URIs listed in the header are source resources which have been
affected by the outstanding method. The status code indicates the
resolution of the method on the identified resource. So, for
example, if a MOVE method on a collection is outstanding and a 102
"Processing" response with a Status-URI response header is returned,
Goland et al. [Page 51]
INTERNET-DRAFT WebDAV April 7, 1998
the included URIs will indicate resources that have had move
attempted on them and what the result was.
8.8 Timeout Request Header
TimeOut = "Timeout" ":" 1#TimeType
TimeType = ("Second-" DAVTimeOutVal | "Infinite" | Other)
DAVTimeOutVal = 1*digit
Other = Extend field-value ; See section 4.2 of [Fielding et al.,
1997]
Clients may include Timeout headers in their LOCK requests.
However, the server is not required to honor or even consider these
requests. Clients MUST NOT submit a Timeout request header with any
method other than a LOCK method.
A Timeout request header MUST contain at least one TimeType and may
contain multiple TimeType entries. The purpose of listing multiple
TimeType entries is to indicate multiple different values and value
types that are acceptable to the client. The client lists the
TimeType entries in order of preference.
Timeout response valuse MUST use a Second value, Infinite, or a
TimeType the client has indicated familiarity with. The server may
assume a client is familiar with any TimeType submitted in a Timeout
header.
The "Second" TimeType specifies the number of seconds that will
elapse between granting of the lock at the server, and the automatic
removal of the lock. The timeout value for timetype "Second" MUST
NOT be greater than 2^32-1.
The timeout counter SHOULD be restarted any time an owner of the
lock sends a method to any member of the lock, including unsupported
methods, or methods which are unsuccessful. However the lock MUST
be refreshed if a refresh LOCK method is successfully received.
If the timeout expires then the lock may be lost. Specifically, if
the server wishes to harvest the lock upon time-out, the server
SHOULD act as if an UNLOCK method was executed by the server on the
resource using the lock token of the timed-out lock, performed with
its override authority. Thus logs should be updated with the
disposition of the lock, notifications should be sent, etc., just as
they would be for an UNLOCK request.
Servers are advised to pay close attention to the values submitted
by clients, as they will be indicative of the type of activity the
client intends to perform. For example, an applet running in a
browser may need to lock a resource, but because of the instability
of the environment within which the applet is running, the applet
may be turned off without warning. As a result, the applet is
likely to ask for a relatively small timeout value so that if the
Goland et al. [Page 52]
INTERNET-DRAFT WebDAV April 7, 1998
applet dies, the lock can be quickly harvested. However, a document
management system is likely to ask for an extremely long timeout
because its user may be planning on going off-line.
A client MUST NOT assume that just because the time-out has expired
the lock has been lost.
9 Status Code Extensions to HTTP/1.1
The following status codes are added to those defined in HTTP/1.1
[Fielding et al., 1997].
9.1 102 Processing
Methods can potentially take a long period of time to process,
especially methods that support the Depth header. In such cases the
client may time-out the connection while waiting for a response. To
prevent this the server may return a 102 status code to indicate to
the client that the server is still processing the method.
If a method is taking longer than 20 seconds (a reasonable, but
arbitrary value) to process the server SHOULD return a 102
"Processing" response.
9.2 207 Multi-Status
The response provides status for multiple independent operations.
9.3 422 Unprocessable Entity
The server understands the content type of the request entity, but
was unable to process the contained instructions.
9.4 423 Locked
The source or destination resource of a method is locked.
9.5 424 Method Failure
The method was not executed on a particular resource within its
scope because some part of the method's execution failed causing the
entire method to be aborted. For example, if a command in a
PROPPATCH method fails then, at minimum, the rest of the commands
will also fail with 424 Method Failure.
9.6 425 Insufficient Space on Resource
The resource does not have sufficient space to record the state of
the resource after the execution of this method.
Goland et al. [Page 53]
INTERNET-DRAFT WebDAV April 7, 1998
10 Multi-Status Response
The default 207 Multi-Status response body is a text/xml HTTP entity
that contains a single XML element called multistatus, which
contains a set of XML elements called response which contain 200,
300, 400, and 500 series status codes generated during the method
invocation. 100 series status codes SHOULD NOT be recorded in a
response XML element.
11 XML Element Definitions
In the section below, the final line of each section gives the
element type declaration using the format defined in [Bray, Paoli,
Sperberg-McQueen, 1998]. The "Value" field, where present, specifies
futher restrictions on the allowable contents of the XML element
using BNF (i.e., to further restrict the values of a PCDATA
element).
11.1 activelock XML Element
Name: activelock
Namespace: DAV:
Purpose: Describes a lock on a resource.
11.1.1 depth XML Element
Name: depth
Namespace: DAV:
Purpose: The value of the depth header used to create a lock.
Value: "0" | "infinity"
11.1.2 locktoken XML Element
Name: locktoken
Namespace: DAV:
Purpose: The lock token associated with a lock.
Description: The href contains one or more opaque lock token URIs
which all refer to the same lock (i.e., the OpaqueLockToken-URI
production in section 5.4).
11.1.3 timeout XML Element
Name: timeout
Namespace: DAV:
Purpose: The timeout associated with a lock
Goland et al. [Page 54]
INTERNET-DRAFT WebDAV April 7, 1998
Value: TimeType ;Defined in section 8.8
11.2 collection XML Element
Name: collection
Namespace: DAV:
Purpose: Identifies the associated resource as a collection. The
resourcetype property of a collection resource MUST have this value.
11.3 href XML Element
Name: href
Namespace: DAV:
Purpose: Identifies the content of the element as a URI.
Value: URI ; See section 3.2.1 of [Fielding et al., 1997]
11.4 link XML Element
Name: link
Namespace: DAV:
Purpose: Identifies the property as a link and contains the
source and destination of that link.
Description: The link XML element is used to provide the sources and
destinations of a link. The name of the property containing the
link XML element provides the type of the link. Link is a multi-
valued element, so multiple links may be used together to indicate
multiple links with the same type. The values in the href XML
elements inside the src and dst XML elements of the link XML element
MUST NOT be rejected if they point to resources which do not exist.
11.4.1 dst XML Element
Name: dst
Namespace: DAV:
Purpose: Indicates the destination of a link
Value: URI
11.4.2 src XML Element
Name: src
Namespace: DAV:
Purpose: Indicates the source of a link.
Goland et al. [Page 55]
INTERNET-DRAFT WebDAV April 7, 1998
Value: URI
11.5 lockentry XML Element
Name: lockentry
Namespace: DAV:
Purpose: Defines the types of locks that can be used with the
resource.
11.6 lockinfo XML Element
Name: lockinfo
Namespace: DAV:
Purpose: The lockinfo XML element is used with a LOCK method to
specify the type of lock the client wishes to have created.
11.7 lockscope XML Element
Name: lockscope
Namespace: DAV:
Purpose: Specifies whether a lock is an exclusive lock, or a
shared lock.
11.7.1 exclusive XML Element
Name: exclusive
Namespace: DAV:
Purpose: Specifies an exclusive lock
11.7.2 shared XML Element
Name: shared
Namespace: DAV:
Purpose: Specifies a shared lock
11.8 locktype XML Element
Name: locktype
Namespace: DAV:
Goland et al. [Page 56]
INTERNET-DRAFT WebDAV April 7, 1998
Purpose: Specifies the access type of a lock. At present, this
specification only defines one lock type, the write lock.
11.8.1 write XML Element
Name: write
Namespace: DAV:
Purpose: Specifies a write lock.
11.9 multistatus XML Element
Name: multistatus
Namespace: DAV:
Purpose: Contains multiple response messages.
Description: The responsedescription at the top level is used to
provide a general message describing the overarching nature of the
response. If this value is available an application may use it
instead of presenting the individual response descriptions contained
within the responses.
11.9.1 response XML Element
Name: response
Namespace: DAV:
Purpose: Holds a single response describing the effect of a
method on resource and/or its properties.
Description: A particular href MUST NOT appear more than once as the
child of a response XML element under a multistatus XML element.
This requirement is necessary in order to keep processing costs for
a response to linear time. Essentially, this prevents having to
search in order to group together all the responses by href. There
are, however, no requirements regarding ordering based on href
values.
11.9.1.1 propstat XML Element
Name: propstat
Namespace: DAV:
Purpose: Groups together a prop and status element that is
associated with a particular href element.
Description: The propstat XML element MUST contain one prop XML
element and one status XML element. The contents of the prop XML
Goland et al. [Page 57]
INTERNET-DRAFT WebDAV April 7, 1998
element MUST only list the names of properties to which the result
in the status element applies.
11.9.1.2 status XML Element
Name: status
Namespace: DAV:
Purpose: Holds a single HTTP status-line
Value: status-line ;status-line defined in [Fielding et al.,
1997]
11.9.2 responsedescription XML Element
Name: responsedescription
Namespace: DAV:
Purpose: Contains a message that can be displayed to the user
explaining the nature of the response.
Description: This XML element provides information suitable to be
presented to a user.
11.10 owner XML Element
Name: owner
Namespace: DAV:
Purpose: Provides information about the principal taking out a
lock.
Description: The owner XML element provides information sufficient
for either directly contacting a principal (such as a telephone
number or Email URI), or for discovering the principal (such as the
URL of a homepage) who owns a lock.
11.11 prop XML element
Name: prop
Namespace: DAV:
Purpose: Contains properties related to a resource.
Description: The prop XML element is a generic container for
properties defined on resources. All elements inside a prop XML
element MUST define properties related to the resource. No other
elements may be used inside of a prop element.
Goland et al. [Page 58]
INTERNET-DRAFT WebDAV April 7, 1998
11.12 propertybehavior XML element
Name: propertybehavior
Namespace: DAV:
Purpose: Specifies how properties are handled during a COPY or
MOVE.
Description: The propertybehavior XML element specifies how
properties are handled during a COPY or MOVE. If this XML element
is not included in the request body then the server is expected to
act as defined by the default property handling behavior of the
associated method. All WebDAV compliant resources MUST support the
propertybehavior XML element.
11.12.1 keepalive XML element
Name: keepalive
Namespace: DAV:
Purpose: Specifies requirements for the copying/moving of live
properties.
Description: If a list of URIs is included as the value of keepalive
then the named properties MUST be "live" after they are copied
(moved) to the destination resource of a COPY (or MOVE). If the
value "*" is given for the keepalive XML element, this designates
that all live properties on the source resource MUST be live on the
destination. If the requirements specified by the keepalive element
can not be honored then the method MUST fail with a 412 Precondition
Failed. All DAV compliant resources MUST support the keepalive XML
element for use with the COPY and MOVE methods.
Value: "*" ; #PCDATA value can only be "*"
11.12.2 omit XML element
Name: omit
Namespace: DAV:
Purpose: The omit XML element instructs the server that it should
use best effort to copy properties but a failure to copy a property
MUST NOT cause the method to fail.
Description: The default behavior for a COPY or MOVE is to copy/move
all properties or fail the method. In certain circumstances, such
as when a server copies a resource over another protocol such as
FTP, it may not be possible to copy/move the properties associated
with the resource. Thus any attempt to copy/move over FTP would
always have to fail because properties could not be moved over, even
as dead properties. All DAV compliant resources MUST support the
omit XML element on COPY/MOVE methods.
Goland et al. [Page 59]
INTERNET-DRAFT WebDAV April 7, 1998
11.13 propertyupdate XML element
Name: propertyupdate
Namespace: DAV:
Purpose: Contains a request to alter the properties on a
resource.
Description: This XML element is a container for the information
required to modify the properties on the resource. This XML element
is multi-valued.
11.13.1 remove XML element
Name: remove
Namespace: DAV:
Purpose: Lists the DAV properties to be removed from a resource.
Description: Remove instructs that the properties specified in prop
should be removed. Specifying the removal of a property that does
not exist is not an error. All the XML elements in a prop XML
element inside of a remove XML element MUST be empty, as only the
names of properties to be removed are required.
11.13.2 set XML element
Name: set
Namespace: DAV:
Purpose: Lists the DAV property values to be set for a resource.
Description: The set XML element MUST contain only a prop XML
element. The elements contained by the prop XML element inside the
set XML element MUST specify the name and value of properties that
are set on the Request-URI. If a property already exists then its
value is replaced.
11.14 propfind XML Element
Name: propfind
Namespace: DAV:
Purpose: Specifies the properties to be returned from a PROPFIND
method. Two special elements are specified for use with propfind,
allprop and propname. If prop is used inside propfind it MUST only
contain property names, not values.
Goland et al. [Page 60]
INTERNET-DRAFT WebDAV April 7, 1998
11.14.1 allprop XML Element
Name: allprop
Namespace: DAV:
Purpose: The allprop XML element specifies that all property
names and values on the resource are to be returned.
11.14.2 propname XML Element
Name: propname
Namespace: DAV:
Purpose: The propname XML element specifies that only a list of
property names on the resource is to be returned.
12 DAV Properties
For DAV properties, the name of the property is also the same as the
name of the XML element that contains its value. In the section
below, the final line of each section gives the element type
declaration using the format defined in [Bray, Paoli, Sperberg-
McQueen, 1998]. The "Value" field, where present, specifies futher
restrictions on the allowable contents of the XML element using BNF
(i.e., to further restrict the values of a PCDATA element).
12.1 creationdate Property
Name: creationdate
Namespace: DAV:
Purpose: Records the time and date the resource was created.
Value: date-time ; See Appendix 2
Description: The creationdate property should be defined on all DAV
compliant resources. If present, it contains a timestamp of the
moment when the resource was created (i.e., the moment it had non-
null state).
12.2 displayname Property
Name: displayname
Namespace: DAV:
Purpose: Provides a name for the resource that is suitable for
presentation to a user.
Description: The displayname property should be defined on all DAV
compliant resources. If present, the property contains a
description of the resource that is suitable for presentation to a
user.
Goland et al. [Page 61]
INTERNET-DRAFT WebDAV April 7, 1998
12.3 getcontentlanguage Property
Name: getcontentlanguage
Namespace: DAV:
Purpose: Contains the Content-Language header returned by a GET
without accept headers
Description: The getcontentlanguage property MUST be defined on any
DAV compliant resource that returns the Content-Language header on a
GET.
Value: language-tag ;language-tag is defined in section 14.13
of [Fielding et al., 1997]
12.4 getcontentlength Property
Name: getcontentlength
Namespace: DAV:
Purpose: Contains the Content-Length header returned by a GET
without accept headers.
Description: The getcontentlength property MUST be defined on any
DAV compliant resource that returns the Content-Length header in
response to a GET.
Value: content-length ; see section 14.14 of [Fielding et al.,
1997]
12.5 getcontenttype Property
Name: getcontenttype
Namespace: DAV:
Purpose: Contains the Content-Type header returned by a GET
without accept headers.
Description: This getcontenttype property MUST be defined on any DAV
compliant resource that returns the Content-Type header in response
to a GET.
Value: media-type ; defined in section 3.7 of [Fielding et
al., 1997]
12.6 getetag Property
Name: getetag
Namespace: DAV:
Purpose: Contains the ETag header returned by a GET without
accept headers.
Description: Note that the ETag on a resource may reflect changes in
any part of the state of the resource, not necessarily just a change
Goland et al. [Page 62]
INTERNET-DRAFT WebDAV April 7, 1998
to the response to the GET method. For example, a change to a
resource's access permissions may cause the ETag to change. The
getetag property MUST be defined on any DAV compliant resource that
returns the Etag header in response to a GET.
Value: entity-tag ; defined in section 3.11 of [Fielding et
al., 1997]
12.7 getlastmodified Property
Name: getlastmodified
Namespace: DAV:
Purpose: Contains the Last-Modified header returned by a GET
method without accept headers.
Description: Note that the last-modified date on a resource may
reflect changes in any part of the state of the resource, not
necessarily just a change to the response to the GET method. For
example, a change in a property may cause the last-modified date to
change. The getlastmodified property MUST be defined on any DAV
compliant resource that returns the Last-Modified header in response
to a GET.
Value: HTTP-date ; defined in section 3.3.1 of [Fielding et
al., 1997]
12.8 lockdiscovery Property
Name: lockdiscovery
Namespace: DAV:
Purpose: Describes the active locks on a resource
Description: The lockdiscovery property returns a listing of who has
a lock, what type of lock he has, the timeout type and the time
remaining on the timeout, and the associated lock token. The server
is free to withhold any or all of this information if the requesting
principal does not have sufficient access rights to see the
requested data.
12.8.1 Example - Retrieving the lockdiscovery Property
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Content-Length: xxxx
Content-Type: text/xml
Goland et al. [Page 63]
INTERNET-DRAFT WebDAV April 7, 1998
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxxx
http://www.foo.bar/container/0Jane SmithInfinite
opaquelocktoken:f81de2ad-7f3d-a1b2-4f3c-00a0c91a9d76
HTTP/1.1 200 OK
This resource has a single exclusive write lock on it, with an
infinite timeout.
12.9 resourcetype Property
Name: resourcetype
Namespace: DAV:
Purpose: Specifies the nature of the resource.
Description: The resourcetype property MUST be defined on all DAV
compliant resources. The default value is empty.
Goland et al. [Page 64]
INTERNET-DRAFT WebDAV April 7, 1998
12.10 source Property
Name: source
Namespace: DAV:
Purpose: The destination of the source link identifies the
resource that contains the unprocessed source of the link's source.
Description: The source of the link (src) is typically the URI of
the output resource on which the link is defined, and there is
typically only one destination (dst) of the link, which is the URI
where the unprocessed source of the resource may be accessed. When
more than one link destination exists, this specification asserts no
policy on ordering.
12.10.1 Example - A source Property
Sourcehttp://foo.bar/programhttp://foo.bar/src/main.cLibraryhttp://foo.bar/programhttp://foo.bar/src/main.libMakefilehttp://foo.bar/programhttp://foo.bar/src/makefile
In this example the resource http://foo.bar/program has a source
property that contains three links. Each link contains three
elements, two of which, src and dst, are part of the DAV schema
defined in this document, and one which is defined by the schema
http://www.foocorp.com/project/ (Source, Library, and Makefile). A
client which only implements the elements in the DAV spec will not
understand the foocorp elements and will ignore them, thus seeing
the expected source and destination links. An enhanced client may
know about the foocorp elements and be able to present the user with
additional information about the links. This example demonstrates
the power of XML markup, allowing element values to be enhanced
without breaking older clients.
Goland et al. [Page 65]
INTERNET-DRAFT WebDAV April 7, 1998
12.11 supportedlock Property
Name: supportedlock
Namespace: DAV:
Purpose: To provide a listing of the lock capabilities supported
by the resource.
Description: The supportedlock property of a resource returns a
listing of the combinations of scope and access types which may be
specified in a lock request on the resource. Note that the actual
contents are themselves controlled by access controls so a server is
not required to provide information the client is not authorized to
see.
12.11.1 Example - Retrieving the supportedlock Property
>>Request
PROPFIND /container/ HTTP/1.1
Host: www.foo.bar
Content-Length: xxxx
Content-Type: text/xml
Goland et al. [Page 66]
INTERNET-DRAFT WebDAV April 7, 1998
>>Response
HTTP/1.1 207 Multi-Status
Content-Type: text/xml
Content-Length: xxxxx
http://www.foo.bar/container/HTTP/1.1 200 OK
13 DAV XML Processing Instructions
All DAV compliant resources MUST ignore any unknown XML element and
all its children encountered while processing a DAV method that uses
XML as its command language.
This restriction also applies to the processing, by clients, of DAV
property values where unknown XML elements SHOULD be ignored unless
the property's schema declares otherwise.
This restriction does not apply to setting dead DAV properties on
the server where the server MUST record unknown XML elements.
Additionally, this restriction does not apply to the use of XML
where XML happens to be the content type of the entity body, for
example, when used as the body of a PUT.
14 DAV Compliance Classes
A DAV compliant resource can choose from two classes of compliance.
A client can discover the compliance classes of a resource by
Goland et al. [Page 67]
INTERNET-DRAFT WebDAV April 7, 1998
executing OPTIONS on the resource, and examining the "DAV" header
which is returned.
Since this document describes extensions to the HTTP/1.1 protocol,
minimally all DAV compliant resources, clients, and proxies MUST be
compliant with [Fielding et al., 1997].
Compliance classes are not necessarily sequential. A resource that
is class 2 compliant must also be class 1 compliant; but if
additional compliance classes are defined later, a resource that is
class 1, 2, and 4 compliant might not be class 3 compliant. Also
note that identifiers other than numbers may be used as compliance
class identifiers.
14.1 Class 1
A class 1 compliant resource MUST meet all "MUST" requirements in
all sections of this document.
Class 1 compliant resources MUST return, at minimum, the value "1"
in the DAV header on all responses to the OPTIONS method.
14.2 Class 2
A class 2 compliant resource MUST meet all class 1 requirements and
support the LOCK method, the supportedlock property, the
lockdiscovery property, the Time-Out response header and the Lock-
Token request header. A class "2" compliant resource SHOULD also
support the Time-Out request header and the owner XML element.
Class 2 compliant resources MUST return, at minimum, the values "1"
and "2" in the DAV header on all responses to the OPTIONS method.
15 Internationalization Considerations
In the realm of internationalization, this specification complies
with the IETF Character Set Policy [Alvestrand, 1998]. In this
specification, human-readable fields can be found either in the
value of a property, or in an error message returned in a response
entity body. In both cases, the human-readable content is encoded
using XML, which has explicit provisions for character set tagging
and encoding, and requires that XML processors read XML elements
encoded, at minimum, using the UTF-8 [Yergeau, 1998] encoding of the
ISO 10646 multilingual plane.
XML also provides a language tagging capability for specifying the
language of the contents of a particular XML element. XML uses
either IANA registered language tags (see RFC 1766, [Alvestrand,
1995]) or ISO 639 language tags [ISO-639] in the "xml:lang"
attribute of an XML element to identify the language of its content
and attributes.
Goland et al. [Page 68]
INTERNET-DRAFT WebDAV April 7, 1998
WebDAV applications MUST support the character set tagging,
character set encoding, and the language tagging functionality of
the XML specification.
Names used within this specification fall into three categories:
names of protocol elements such as methods and headers, names of XML
elements, and names of properties. Naming of protocol elements
follows the precedent of HTTP, using English names encoded in
USASCII for methods and headers. Since these protocol elements are
not visible to users, and are in fact simply long token identifiers,
they do not need to support encoding in multiple character sets.
Similarly, though the names of XML elements used in this
specification are English names encoded in UTF-8, these names are
not visible to the user, and hence do not need to support multiple
character set encodings.
The name of a property defined on a resource is a URI. Although
some applications (e.g., a generic property viewer) will display
property URIs directly to their users, it is expected that the
typical application will use a fixed set of properties, and will
provide a mapping from the property name URI to a human-readable
field when displaying the property name to a user. It is only in
the case where the set of properties is not known ahead of time that
an application need display a property name URI to a user. We
recommend that applications provide human-readable property names
wherever feasible.
For error reporting, we follow the convention of HTTP/1.1 status
codes, including with each status code a short, English description
of the code (e.g., 423 Locked). While the possibility exists that a
poorly crafted user agent would display this message to a user,
internationalized applications will ignore this message, and display
an appropriate message in the user's language and character set.
Since interoperation of clients and servers does not require locale
information, this specification does not specify any mechanism for
transmission of this information.
16 Security Considerations
This section is provided to detail issues concerning security
implications of which WebDAV applications need to be aware.
All of the security considerations of HTTP/1.1 also apply to WebDAV.
In addition, the security risks inherent in remote authoring require
stronger authentication technology, introduce several new privacy
concerns, and may increase the hazards from poor server design.
These issues are detailed below.
16.1 Authentication of Clients
Goland et al. [Page 69]
INTERNET-DRAFT WebDAV April 7, 1998
Due to their emphasis on authoring, WebDAV servers need to use
authentication technology to protect not just access to a network
resource, but the integrity of the resource as well. Furthermore,
the introduction of locking functionality requires support for
authentication.
A password sent in the clear over an insecure channel is an
inadequate means for protecting the accessibility and integrity of a
resource as the password may be intercepted. Since Basic
authentication for HTTP/1.1 performs essentially clear text
transmission of a password, Basic authentication MUST NOT be used to
authenticate a WebDAV client to a server unless the connection is
secure. Furthermore, a WebDAV server MUST NOT send Basic
authentication credentials in a WWW-Authenticate header unless the
connection is secure. Examples of secure connections include a
Transport Layer Security (TLS) connection, or a connection over a
network which is physically secure, for example, an isolated network
in a building with restricted access.
WebDAV applications MUST support the Digest authentication scheme
[Franks et al., 1997]. Since Digest authentication verifies that
both parties to a communication know a shared secret, a password,
without having to send that secret in the clear, Digest
authentication avoids the security problems inherent in Basic
authentication while providing a level of authentication which is
useful in a wide range of scenarios.
16.2 Denial of Service
Denial of service attacks are of special concern to WebDAV servers.
WebDAV plus HTTP enables denial of service attacks on every part of
a system's resources.
The underlying storage can be attacked by PUTting extremely large
files.
Asking for recursive operations on large collections can attack
processing time.
Making multiple pipelined requests on multiple connections can
attack network connections.
WebDAV servers need to be aware of the possibility of a denial of
service attack at all levels.
16.3 Security through Obscurity
WebDAV provides, through the PROPFIND method, a mechanism for
listing the member resources of a collection. This greatly
diminishes the effectiveness of security or privacy techniques that
rely only on the difficulty of discovering the names of network
resources. Users of WebDAV servers are encouraged to use access
Goland et al. [Page 70]
INTERNET-DRAFT WebDAV April 7, 1998
control techniques to prevent unwanted access to resources, rather
than depending on the relative obscurity of their resource names.
16.4 Privacy Issues Connected to Locks
When submitting a lock request a user agent may also submit an owner
XML field giving contact information for the person taking out the
lock (for those cases where a person, rather than a robot, is taking
out the lock). This contact information is stored in a lockdiscovery
property on the resource, and can be used by other collaborators to
begin negotiation over access to the resource. However, in many
cases this contact information can be very private, and should not
be widely disseminated. Servers SHOULD limit read access to the
lockdiscovery property as appropriate. Furthermore, user agents
SHOULD provide control over whether contact information is sent at
all, and if contact information is sent, control over exactly what
information is sent.
16.5 Privacy Issues Connected to Properties
Since property values are typically used to hold information such as
the author of a document, there is the possibility that privacy
concerns could arise stemming from widespread access to a resource's
property data. To reduce the risk of inadvertent release of private
information via properties, servers are encouraged to develop access
control mechanisms that separate read access to the resource body
and read access to the resource's properties. This allows a user to
control the dissemination of their property data without overly
restricting access to the resource's contents.
16.6 Reduction of Security due to Source Link
HTTP/1.1 warns against providing read access to script code because
it may contain sensitive information. Yet WebDAV, via its source
link facility, can potentially provide a URL for script resources so
they may be authored. For HTTP/1.1, a server could reasonably
prevent access to source resources due to the predominance of read-
only access. WebDAV, with its emphasis on authoring, encourages
read and write access to source resources, and provides the source
link facility to identify the source. This reduces the security
benefits of eliminating access to source resources. Users and
administrators of WebDAV servers should be very cautious when
allowing remote authoring of scripts, limiting read and write access
to the source resources to authorized principals.
17 IANA Considerations
This document defines two namespaces, the namespace of property
names, and the namespace of WebDAV-specific XML elements used within
property values.
Goland et al. [Page 71]
INTERNET-DRAFT WebDAV April 7, 1998
URLs are used for both names, for several reasons. Assignment of a
URL does not require a request to a central naming authority, and
hence allow WebDAV property names and XML elements to be quickly
defined by any WebDAV user or application. URLs also provide a
unique address space, ensuring that the distributed users of WebDAV
will not have collisions among the property names and XML elements
they create.
This specification defines a distinguished set of property names and
XML elements that are understood by all WebDAV applications. The
property names and XML elements in this specification are all
derived from the base URI DAV: by adding a suffix to this URI, for
example, DAV:creationdate for the "creationdate" property.
This specification also defines a URI scheme for the encoding of
lock tokens, the opaquelocktoken URI scheme described in section
5.4.
To ensure correct interoperation based on this specification, IANA
must reserve the URI namespaces starting with "DAV:" and with
"opaquelocktoken:" for use by this specification, its revisions, and
related WebDAV specifications.
18 Terminology
Collection - A resource that contains member resources and meets the
requirements in section 4 of this specification.
Member Resource - A resource contained by a collection.
Internal Member Resource - A member resource of a collection whose
URI is relative to the URI of the collection.
Property - A name/value pair that contains descriptive information
about a resource.
Live Property - A property whose semantics and syntax are enforced
by the server. For example, a live "content-length" property would
have its value, the length of the entity returned by a GET request,
automatically calculated by the server.
Dead Property - A property whose semantics and syntax are not
enforced by the server. The server only records the value of a dead
property; the client is responsible for maintaining the consistency
of the syntax and semantics of a dead property.
Null Resource - A resource which responds with a 404 Not Found to
any HTTP/1.1 or DAV method except for PUT, MKCOL, OPTIONS and LOCK.
A NULL resource MUST NOT appear as a member of its parent
collection.
Goland et al. [Page 72]
INTERNET-DRAFT WebDAV April 7, 1998
19 Copyright
The following copyright notice is copied from RFC 2026 [Bradner,
1996], section 10.4, and describes the applicable copyright for this
document.
Copyright (C) The Internet Society April 5, 1998. All Rights
Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
20 Intellectual Property
The following notice is copied from RFC 2026 [Bradner, 1996],
section 10.4, and describes the position of the IETF concerning
intellectual property claims made against this document.
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use other technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances
of licenses to be made available, or the result of an attempt made
to obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification
can be obtained from the IETF Secretariat.
Goland et al. [Page 73]
INTERNET-DRAFT WebDAV April 7, 1998
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
21 Acknowledgements
A specification such as this thrives on piercing critical review and
withers from apathetic neglect. The authors gratefully acknowledge
the contributions of the following people, whose insights were so
valuable at every stage of our work.
Terry Allen, Harald Alvestrand, Jim Amsden, Becky Anderson, Alan
Babich, Sanford Barr, Dylan Barrell, Bernard Chester, Tim Berners-
Lee, Dan Connolly, Jim Cunningham, Ron Daniel, Jr., Jim Davis, Keith
Dawson, Mark Day, Brian Deen, Martin Duerst, David Durand, Lee
Farrell, Chuck Fay, Wesley Felter, Roy Fielding, Mark Fisher, Alan
Freier, George Florentine, Jim Gettys, Phill Hallam-Baker, Dennis
Hamilton, Steve Henning, Mead Himelstein, Alex Hopmann, Andre van
der Hoek, Ben Laurie, Paul Leach, Ora Lassila, Karen MacArthur,
Steven Martin, Larry Masinter, Michael Mealling, Keith Moore, Henrik
Nielsen, Kenji Ota, Bob Parker, Glenn Peterson, Jon Radoff, Saveen
Reddy, Henry Sanders, Christopher Seiwald, Judith Slein, Mike
Spreitzer, Einar Stefferud, Ralph Swick, Kenji Takahashi, Richard N.
Taylor, Robert Thau, John Turner, Sankar Virdhagriswaran, Fabio
Vitali, Gregory Woodhouse, and Lauren Wood.
Two from this list deserve special mention. The contributions by
Larry Masinter have been invaluable, both in helping the formation
of the working group and in patiently coaching the authors along the
way. In so many ways he has set high standards we have toiled to
meet. The contributions of Judith Slein in clarifying the
requirements, and in patiently reviewing draft after draft, both
improved this specification and expanded our minds on document
management.
We would also like to thank John Turner for developing the XML DTD.
Goland et al. [Page 74]
INTERNET-DRAFT WebDAV April 7, 1998
22 References
22.1 Normative References
[Alvestrand, 1995] H. T. Alvestrand, "Tags for the Identification of
Languages." RFC 1766. Uninett. March, 1995.
[Alvestrand, 1998] H. T. Alvestrand, "IETF Policy on Character Sets
and Languages." RFC 2277, BCP 18. Uninett. January, 1998.
[Bradner, 1997] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels." RFC 2119, BCP 14. Harvard University. March,
1997.
[Bray, Paoli, Sperberg-McQueen, 1998] T. Bray, J. Paoli, C. M.
Sperberg-McQueen, "Extensible Markup Language (XML)." World Wide Web
Consortium Recommendation REC-xml-19980210.
http://www.w3.org/TR/1998/REC-xml-19980210.
[Franks et al., 1997] J. Franks, P. Hallam-Baker, J. Hostetler, P.
Leach, A. Luotonen, E. Sink, and L. Stewart. "An Extension to HTTP :
Digest Access Authentication" RFC 2069. Northwestern University,
CERN, Spyglass Inc., Microsoft Corp., Netscape Communications Corp.,
Spyglass Inc., Open Market Inc. January 1997.
[Fielding et al., 1997] R. Fielding, J. Gettys, J. Mogul, H.
Frystyk, T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1."
RFC 2068. U.C. Irvine, DEC, MIT/LCS. January, 1997.
[ISO-639] ISO (International Organization for Standardization). ISO
639:1988. "Code for the representation of names of languages."
[ISO-8601] ISO (International Organization for Standardization). ISO
8601:1988. "Data elements and interchange formats - Information
interchange - Representation of dates and times."
[Leach, Salz, 1998] P. J. Leach, R. Salz, "UUIDs and GUIDs."
Internet-draft, work-in-progress, February, 1998.
ftp://ietf.org/internet-drafts/draft-leach-uuids-guids-01.txt
[Yergeau, 1998] F. Yergeau, "UTF-8, a transformation format of
Unicode and ISO 10646." RFC 2279. Alis Technologies. January, 1998.
22.2 Informational References
[Bradner, 1996] S. Bradner, "The Internet Standards Process -
Revision 3." RFC 2026, BCP 9. Harvard University. October, 1996.
[Bray, Hollander, Layman, 1998] T. Bray, D. Hollander, A. Layman,
"Name Spaces in XML" World Wide Web Consortium Working Draft,
http://www.w3.org/TR/WD-xml-names.
Goland et al. [Page 75]
INTERNET-DRAFT WebDAV April 7, 1998
[Lasher, Cohen, 1995] R. Lasher, D. Cohen, "A Format for
Bibliographic Records," RFC 1807. Stanford, Myricom. June, 1995.
[MARC, 1994] Network Development and MARC Standards, Office, ed.
1994. "USMARC Format for Bibliographic Data", 1994. Washington, DC:
Cataloging Distribution Service, Library of Congress.
[Miller et al., 1996] J. Miller, T. Krauskopf, P. Resnick, W.
Treese, "PICS Label Distribution Label Syntax and Communication
Protocols" Version 1.1, World Wide Web Consortium Recommendation
REC-PICS-labels-961031. http://www.w3.org/pub/WWW/TR/REC-PICS-
labels-961031.html.
[Slein et al., 1998] J. A. Slein, F. Vitali, E. J. Whitehead, Jr.,
D. Durand, "Requirements for Distributed Authoring and Versioning
Protocol for the World Wide Web." RFC 2291. Xerox, Univ. of Bologna,
U.C. Irvine, Boston Univ. February, 1998.
[Weibel et al., 1995] S. Weibel, J. Godby, E. Miller, R. Daniel,
"OCLC/NCSA Metadata Workshop Report."
http://purl.oclc.org/metadata/dublin_core_report.
Goland et al. [Page 76]
INTERNET-DRAFT WebDAV April 7, 1998
23 Authors' Addresses
Y. Y. Goland
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
Email: yarong@microsoft.com
E. J. Whitehead, Jr.
Dept. Of Information and Computer Science
University of California, Irvine
Irvine, CA 92697-3425
Email: ejw@ics.uci.edu
A. Faizi
Netscape
685 East Middlefield Road
Mountain View, CA 94043
Email: asad@netscape.com
S. R. Carter
Novell
1555 N. Technology Way
M/S ORM F111
Orem, UT 84097-2399
Email: srcarter@novell.com
D. Jensen
Novell
1555 N. Technology Way
M/S ORM F111
Orem, UT 84097-2399
Email: dcjensen@novell.com
Goland et al. [Page 77]
INTERNET-DRAFT WebDAV April 7, 1998
24 Appendices
24.1 Appendix 1 - WebDAV Document Type Definition
This section provides a document type definition, following the
rules in [Bray, Paoli, Sperberg-McQueen, 1998], for the XML elements
used in the protocol stream and in the values of properties. It
collects the element definitions given in sections 11 and 12.
Goland et al. [Page 78]
INTERNET-DRAFT WebDAV April 7, 1998
]>
24.2 Appendix 2 - ISO 8601 Date and Time Profile
The creationdate property specifies the use of the ISO 8601 date
format [ISO-8601]. This section defines a profile of the ISO 8601
date format for use with this specification. This profile is quoted
verbatim from draft-newman-datetime-01.txt (expired).
date-time = full-date "T" full-time
full-date = date-fullyear "-" date-month "-" date-mday
full-time = partial-time time-offset
date-fullyear = 4DIGIT
date-month = 2DIGIT ; 01-12
date-mday = 2DIGIT ; 01-28, 01-29, 01-30, 01-31 based on
month/year
time-hour = 2DIGIT ; 00-23
time-minute = 2DIGIT ; 00-59
time-second = 2DIGIT ; 00-59, 00-60 based on leap second rules
time-secfrac = "." 1*DIGIT
time-numoffset = ("+" / "-") time-hour ":" time-minute
time-offset = "Z" / time-numoffset
partial-time = time-hour ":" time-minute ":" time-second
Goland et al. [Page 79]
INTERNET-DRAFT WebDAV April 7, 1998
[time-secfrac]
Numeric offsets are calculated as local time minus UTC (Coordinated
Universal Time). So the equivalent time in UTC can be determined by
subtracting the offset from the local time. For example, 18:50:00-
04:00 is the same time as 22:58:00Z.
If the time in UTC is known, but the offset to local time is
unknown, this can be represented with an offset of "-00:00". This
differs from an offset of "Z" which implies that UTC is the
preferred reference point for the specified time.
24.3 Appendix 3 - Notes on Processing XML Elements
24.3.1 Notes on Empty XML Elements
XML supports two mechanisms for indicating that an XML element does
not have any content. The first is to declare an XML element of the
form . The second is to declare an XML element of the form
. The two XML elements are semantically identical.
It is a violation of the XML specification to use the form
if the associated DTD declares the element to be EMPTY (e.g.,
). If such a statement is included, then the
empty element format, must be used. If the element is not
delcared to be EMPTY, then either form or may be used
for empty elements.
24.3.2 Notes on Illegal XML Processing
XML is a flexible data format that makes it easy to submit data that
appears legal but in fact is not. The philosophy of "Be flexible in
what you accept and strict in what you send" still applies, but it
must not be applied inappropriately. XML is extremely flexible in
dealing with issues of white space, element ordering, inserting new
elements, etc. This flexibility does not require extension,
especially not in the area of the meaning of elements.
There is no kindness in accepting illegal combinations of XML
elements. At best it will cause an unwanted result and at worst it
can cause real damage.
24.3.2.1 Example - XML Syntax Error
The following request body for a PROPFIND method is illegal.
Goland et al. [Page 80]
INTERNET-DRAFT WebDAV April 7, 1998
The definition of the propfind element only allows for the allprop
or the propname element, not both. Thus the above is an error and
must be responded to with a 400 Bad Request.
Imagine, however, that a server wanted to be "kind" and decided to
pick the allprop element as the true element and respond to it. A
client running over a bandwidth limited line who intended to execute
a propname would be in for a big surprise if the server treated the
command as an allprop.
Additionally, if a server were lenient and decided to reply to this
request, the results would vary randomly from server to server, with
some servers executing the allprop directive, and others executing
the propname directive. This reduces interoperability rather than
increasing it.
24.3.2.2 Example - Unknown XML Element
The previous example was illegal because it contained two elements
that were explicitly banned from appearing together in the propfind
element. However, XML is an extensible language, so one can imagine
new elements being defined for use with propfind. Below is the
request body of a PROPFIND and, like the previous example, must be
rejected with a 400 Bad Request by a server that does not understand
the expired-props element.
To understand why a 400 Bad Request is returned let us look at the
request body as the server unfamiliar with expired-props sees it.
As the server does not understand the expired-props element, by the
rules of XML, it must ignore it. Thus the server sees an empty
propfind, which by the definition of the propfind element is
illegal.
Goland et al. [Page 81]
INTERNET-DRAFT WebDAV April 7, 1998
Please note that had the extension been additive it would not
necessarily have resulted in a 400 Bad Request. For example,
imagine the following request body for a PROPFIND:
*boss*
The previous example contains the fictitious element leave-out. Its
purpose is to prevent the return of any property whose name matches
the submitted pattern. If the previous example were submitted to a
server unfamiliar with leave-out, the only result would be that the
leave-out element would be ignored and a propname would be executed.
24.4 Appendix 4 -- XML Namespaces for WebDAV
24.4.1 Introduction
To provide a unique space of XML element names which has
decentralized extensibility, this specification uses a feature of
XML known as XML "namespaces". This appendix provides a normative
reference for XML namespace functionality for implementations of
this specification. All DAV compliant systems MUST support the XML
namespace extension as specified in this appendix.
The remainder of this appendix is intended to match, as closely as
needed, the text in WD-xml-names-19980327, "Namespaces in XML",
edited by Tim Bray, Dave Hollander, and Andrew Layman [Bray,
Hollander, Layman, 1998]. To meet this goal, the text in this
appendix is mostly quoted verbatim from that source. The notational
conventions and BNF productions in this appendix match those of the
XML specification [Bray, Paoli, Spreberg-McQueen, 1998]
XML namespaces are based on the use of qualified names, which
contain a single colon, separating the name into a namespace prefix
and the local name. The prefix, which is mapped to a URI, selects a
namespace. The combination of the universally-managed URI namespace
and the local schema namespace produces names that are guaranteed
universally unique.
URIs can contain characters not allowed in names, and so cannot be
used directly as namespace prefixes. Therefore, the namespace
prefix serves as a proxy for a URI. A special processing
instruction described below is used to declare the association of
the namespace prefix with a URI; software which supports this
namespace proposal must recognize and act on it.
Goland et al. [Page 82]
INTERNET-DRAFT WebDAV April 7, 1998
A namespace is declared using a reserved processing instruction as
follows:
24.4.2 Namespace Declaration PI
[1] NamespacePI ::= '' [ NSC: Required Parts ]
[2] NSDef ::= 'ns' Eq SystemLiteral [ NSC: No Fragments ]
[3] SrcDef ::= 'src' Eq SystemLiteral
[4] PrefixDef ::= 'prefix' Eq ("'" NCName "'" | '"' NCName '"')
[5] NCName ::= (Letter | '_') (NCNameChar)* /* An XML Name, minus
the ":" */
[6] NCNameChar ::= Letter | Digit | '.' | '-' | '_' |
CombiningChar | Extender
[Definition:] The SystemLiteral in the NSDef production is a URI
which functions as a namespace name to identify the namespace. The
SystemLiteral in the SrcDef production is an optional URI which may
be used to retrieve the schema, if one is provided. Some namespaces
need no schemas; this specification does not depend on their
existence, or on the use of any particular machine- or human-
readable syntax in the schema.
[Definition:] The NCName in the PrefixDef production gives the
namespace prefix used to associate names in an XML document with
this namespace.
Namespace Constraint: Required Parts
A namespace declaration must contain exactly one NSDef, exactly one
PrefixDef and zero or one SrcDef.
Namespace Constraint: No Fragments
The SystemLiteral in the NSDef production must contain a URI, not
including an attached #-separated fragment identifier.
The namespace name, to serve its intended purpose, should have the
characteristics of uniqueness and persistence. It is not a goal
that it be directly usable for retrieval of a schema (if any
exists).
24.4.2.1 Examples of namespace declarations:
Goland et al. [Page 83]
INTERNET-DRAFT WebDAV April 7, 1998
24.4.3 Placing Declarations in Documents
Namespace declarations must be located in the prolog of an XML
document, after the XML Declaration (if any) and before the DTD (if
any). This effectively makes the scope of namespace prefixes global
to the whole document, including the DTD. It also means that should
a processor wish to insert its own qualified names, it need only
read the namespace declarations from the prolog to be sure of
generating a new, unique, namespace prefix.
In XML documents conforming to this specification, the prolog must
match the following production:
24.4.4 Prolog with Namespace Declarations
[7] prolog ::= XMLDecl? (NamespacePI | Misc)* (doctypedecl Misc*)?
[ NSC: Unique Prefix ]
Note that the namespace declarations are ordinary processing
instructions which the XML processor will pass to the application as
it does any other.
Namespace Constraint: Unique Prefix
A namespace prefix may not be declared more than once; i.e. there
may not be two PrefixDefs which contain the same NCName string.
24.4.5 Qualified Names
[Definition:] In XML documents conforming to this specification,
some names (constructs corresponding to the nonterminal Name) may be
given as qualified names, defined as follows:
Qualified Name
[8] QName ::= (Prefix ':')? LocalPart
[9] Prefix ::= NCName [ NSC: Prefix Declared ]
[10] LocalPart ::= NCName
The Prefix provides the namespace prefix part of the qualified name,
and must be associated with defining schema through the URI in the
applicable namespace declaration.
[Definition:] The LocalPart provides the local name part of the
qualified name.
Namespace Constraint: Prefix Declared
The namespace prefix, unless it is "xml", must have been declared in
a namespace declaration. The namespace prefix xml is reserved and
considered to have been implicitly declared. No other prefix
Goland et al. [Page 84]
INTERNET-DRAFT WebDAV April 7, 1998
beginning with the three-letter sequence x m, l, in any case
combination, is allowed.
24.4.6 Universal Names
[Definition:] For each qualified name, there is a corresponding
universal name, which is an ordered pair containing first, the
namespace name associated with its prefix, and second, its local
name.
A universal name is independent of the prefix in use in any
particular XML document; thus, universal names provide a basis for
comparing named objects located in different XML documents.
24.4.7 Using Qualified Names
In XML documents conforming to this specification, element types are
given as qualified names, as follows. In the productions below, the
nonterminals (STag, ETag, EmptyElement, and Attribute) are taken
from the XML specification [XML]; the productions in all cases match
a subset of the strings matched by those of the same name in the XML
spec.
Start-tag
[11] STag ::= ''
[12] ETag ::= '' QName S? '>'
[13] EmptyElement ::= ''
24.4.8 Processing instruction
Targets are given as qualified names, as follows:
PI Target
[15] PITarget ::= QName [ NSC: Declare Before Use ]
Namespace Constraint: Declare Before Use
When a PI target, aside from that in a namespace declaration PI, is
qualified with a prefix, that prefix must be declared at a location
in the document which precedes its use.
24.4.9 Scope and Meaning of Qualified Names
[Note to the reader: This section does not appear in [Bray,
Hollander, Layman, 1998], but is necessary to avoid ambiguity for
WebDAV XML processors.]
WebDAV compliant XML processors MUST interpret a qualified name as a
URI constructed by appending the LocalPart to the schema URI of the
namespace. The scope of a namespace in a qualified name is limited
Goland et al. [Page 85]
INTERNET-DRAFT WebDAV April 7, 1998
to a single element tag. Every start tag, end tag, or empty XML
element from a namespace MUST include the namespace name in the tag.
Scope Example
Johnny Updraft
In this example, the qualified element name "del:glider" is
interpreted as the URL "http://www.del.jensen.org/glider". Since
the scope of a namespace is limited to a single element, each start
tag, end tag, and empty element tag in the example includes the
short name of the namespace, "del" as part of the qualified name.
Johnny Updraft
Even though this example is syntactically different from the
previous example, it is semantically identical. Each instance of
the namespace name "bar" is replaced with
"http://www.del.jensen.org/" and then appended to the local name for
each element tag. The resulting tag names in this example are
exactly the same as for the previous example.
Johnny Updraft
This example is semantically identical to the two previous ones.
Each instance of the namespace name "foo" is replaced with
"http://www.del.jensen.org/glide" which is then appended to the
local name for each element tag, the resulting tag names are
identical to those in the previous examples.
Goland et al. [Page 86]